Unsurprisingly this habit of mine extends to gaming.
I like to know what the various opportunities are and build a rough framework of goals for a number of timeframes. To do this I require information which for WoW is thankfully abundant. Great sources of information include Wowhead, Wow Insider, Wowpedia, the official website and hundreds of blogs.
With the knowledge I've gained over the last 5+ years of playing, I find it easiest to first define my goals when I am considering rolling a new toon. From there I can choose a realm, a faction and a character class. I do this because experience has taught me that making the wrong choice in any of those three areas results in either wasted time and an abandoned character or the expenditure of cash to transfer factions or realms (or both). This wastage is amplified by the number of characters created in the wrong environment.
Realm Choice Still Matters
Despite the implementation of Cross Realm Zones (CRZ) incorrectly choosing your realm still has repercussions. Four realm types exist, Player versus Environment (PvE or 'Normal'), Player versus Player (PvP), Roleplaying (RP) and Roleplaying Player versus Player (RPvP). Each of these realm types have their own flavour and culture. North American players are spread across three time zones. Realms have different populations and faction balances. All of these factors has an impact on the atmosphere of the realm, the availability of other players, the potential AH market, and the competition for gathered materials, mobs, tameable pets etc. to name but a few things. Your initial choices matter.
For example, if someday you decide you want to join pick up groups for raids you may find yourself extremely dissapointed if you have chosen to roll a character on the small side of a faction imbalanced RPvP realm that operates on Eastern Time and you live on the West Coast. Likewise, if you decide to become an Auction House maven and trade your way to the gold cap, playing a Horde toon on Stormrage(US) is going to put a severe damper on your dreams of riches given the fact that Stormrage is hugely imbalanced in favour of the Alliance and Horde towns are Ghost Towns.
Cross Realm Zones affect much of the world at large, but your chosen server still determines who is available to do things with, when they are available (generally) and who you can buy and sell things to. Further to this, CRZ are not in place for Pandaria or the Darkmoon Faire.
So how do you gather information on realms in order to choose one correctly or at least to minimize the risk of error? The site Wowcensus does contain information on the size, balance and composition of realms. It's information is unfortunately sketchy at best since it relies on players running a small side program while they play to capture information and update their site. It's not clear how many players do this or what the date of the last data is. I tend to take Wowcensus with a huge grain of salt. Their information isn't totally useless, but it definitely requires further confirmation by other methods.
Forums can provide more clues. The types and quantity of posting on official realm forums can tip you off as to the raiding progression, faction balance and population of a server. Fansite forums may contain realm discussions that hint at those things as well. One good example of this was during the latest Ironman Challenge craze. An Alliance guild on Venture Company(US)(PvP) was offering 100,000g to the first person to complete the challenge as an Alliance toon on their server. This tells me two things, the population of Venture Company is heavily weighted towards the Horde and the Alliance side of the server is highly loyal to both server and faction (this offer was clearly a recruiting call).
A more straightforward method of thinning down your realm choices is to simply roll a fresh toon and go have a look see. For Alliance I recommend a Human and for Horde an Orc as these two races have the shortest and fastest trip into their respective capital cities. Once there look around. How many players do you see? How many postings to the chat channels are there, and are you comfortable with it? How many items are posted to the Auction House, what are the general prices like, how much monopolization is there and what sorts of goods are on offer? How many guilds are advertising in the Looking for Guild tool, what types of guilds are there, what size are they, do you see anything that might possibly resemble a good fit for you?
All of this might seem a bit much, but I would rather spend an hour gathering information and making informed decisions than abandoning a character I've invested several (or more) hours in because my realm choice makes my goals exceedingly difficult or impossible to attain.
Your Class Selection MattersChoosing a class is next on the agenda and what you decide to play will affect your goal attainment. My first character, Eccentrica, is a mage. She's been coddled and cosseted and finetuned and I would never delete her, but she has also been the bane of my existence. Levelling her in Old Azeroth was slow and painful and soloing has been necessarily limited. There are simply things I can't do with her and things that have been made more difficult by class changes over time (Water Elemental nerfs included). She does have her own stable of alts of various classes, but shared achievements notwithstanding, its just unsatisfying to achieve something on an alt instead of on a main.
Your class will determine not only what you solo and can't but what roles you can fill should you decide to group and you need to be OK with that. Some classes have assistance from pets/minions which affects questing speed and content soloability. Some classes get free initial mounts and riding training which affects gold expenditure. Some classes get travel speed boosts or self healing abilities or damage reduction. Every class has it's pros and cons, strengths and weaknesses and will alter what and how you do things depending on your goals.
Wowhead has nice class summaries on each of the class pages such as the one for Druids. You get a basic run down of roles, significant abilities and specializations with further links to more information. If I had more information at my fingertips when I first started playing, Eccentrica probably wouldn't be a mage.
It's may also be helpful to know or keep in mind the class distribution of your chosen realm. For instance if you want to be able to raid (outside of LFR) it's probably not wise to level a Shadow Priest if your realm has an insanely high number of Shadow Priests already.
And Finally, Race
Many people would tell you that race is irrelevant or at least a comestic decision only. I would not be one of them.
Racial bonuses can have extreme utility in certain circumstances (Human: Every Man for Himself), can save/earn you more gold (Goblin: Best Deals Anywhere), can impact your survivability (Troll: Regeneration). Each race has multiples bonuses, some which are great and some less so, but each one has utility.
Each race also has access to a different number of total quests. Goblins, Worgen and Pandaren each have unique starting areas and thus a larger total number of quests in game to do. The Night Elf, Blood Elf and Gnome starter areas are visitable by anyone, but the quests there are racial specific. By contrast, any Alliance race can nip over to Northshire Abbey and do the Human starter quests. I'm going to do a series of articles on each zone and will flesh out what can be done by whom as I go along.
On top of this, each race has different starting stats. I found a nice series of charts here which I will simplify on a new page up top at some point (with proper credit given of course). By end game these differences in base stats have little effect, but depending on your goals can help or hinder you.
If perchance you were interested in the Ironman Challenge, base Stamina would be a very important stat for you, as might Agility. A perusal of the tables shows that Night Elves have the highest combined Stam/Agil point distribution (44), and that Hunters and Rogues get the highest combined class bonus to the intial point distribution of Stamina and Agility (+4). An Ironman Night Elf Hunter (with their juicy Shadowmeld racial ability) probably has a far easier go of it than say, a Tauren Priest.
That's a Lot to Think About
Well, maybe. Maybe I put too much stock into considering the details. Time and experience have demonstrated the pitfalls of not doing a little bit of front end work though. Yes, it's true that realm, faction and racial changes are only a click away, but there are other things I'd prefer to spend my money. I really like to avoid fixing my mistakes with money by not making those mistakes to begin with. I for one would love Blizzard forever if they implemented bulk discounts for character transactions, but I don't see that happening in the near future so I go through the process I've outlined above.
Hopefully I've given food for thought. If you would like to know more about realms, classes or races, the following are a few excellent resources: