Hi "Reignmaker" (I'm assuming that's not your actual name. How 'bout an introduction? Or at least a first name

),
I'll try to address some of your questions. Although it seems you've already answered many of them yourself.
Is this site mainly comprised of people from St. Louis?
Registered members are throughout the U.S.A. (and a few other countries, I think). However, it seems the most active on the forum are St. Louis members.
how does someone who knows very little about Aikido, decide what school or Dojo is best for him to learn?
The best choice is the school you like best. Give all the dojos you care to find in St. Louis a visit ... try a class or two to get an initial feel ... then make a decision on which one you'd like to train at for a while. If it's not working out, try another. You may begin to hear stories about how it's not the style or dojo, but the teacher that's important. There's also the overall feeling of the dojo community that might be what you're looking for. Be prepared for the fact that although many dojos have a head instructor, the teaching responsibilities can be spread among senior students. Such is the case at the St. Louis Ki Society.
One of your concerns:
many people involved in Aikido look down on a particular school for one reason or another.
Aikido doesn't hold the monopoly on that one. People can be petty. Even organizations can be. Hopefully, the majority of us attempt not to be.
Another concern: If someone truly commits to learning Aikido, what is the time frame to advance in rank?
It will depend on the dojo. It could take 4 or more years to reach shodan (1st degree black-belt) level. Is this really a concern?
... do instructors allow you to test based on their personal opinions, and is that dictated by how much time a student has invested?
Yes and no. The head or chief instructor's opinion always matters. In fact, some students are "asked" to test even if that student doesn't necessarily feel they are ready. There are also minimum requirements that need to be satisfied (classes and months trained). However, previous aikido experience is taken into account.
I am from St. Louis, if anyone has a recommendation on an excellent school ...
Being biased, I would recommend the
St. Louis Ki Society.
Mark Rubbert is the head instructor. He has 24-or-so years training in aikido and holds the rank of godan (5th degree blackbelt). A listing of St. louis dojos can be found
here. Just type in Saint Louis, choose state and country, and you're off!
The "black-pants" or hakama, are usually worn by students at brown belt or shodan level and above. Some schools don't bother with them. Others allow all ranks to wear them. It depends. Usually, you can begin training with just a sturdy pair of sweats. At our dojo a "uniform" is not a requirement to begin training.
Please feel free to ask all the questions you want. And good luck!
thanks,
Adam