Hello Knitterman -
I have been in an around San Marcos for over 25 years, but have only lived here for the past two. I really enjoy the attitude and feel that this town has. I currently attend Texas State University and own a house here.
Important things - hmm... well,
It's Texas State, not TSU.
Tubing. When the weather's nice (a good portion of the year), grab a tube and float down the San Marcos river. Rio Vista Park is really nice, and the atmosphere is really friendly and welcoming. Even if you aren't an outdoor/water person, you have to do it at least once!
Trains - we got'em, and they almost always hinder your travel when you're in a hurry. Not really, but that's the way it seems. So if you know you'll be crossing tracks, you may want to add a few minutes to your travel just in case.
Local Businesses. There are a lot, especially restaurants. I'm on campus on Tues/Thurs and have a nice lunch break from 12-2 and have made it my goal to hit as many restaurants in the downtown area as possible. I'd rather give them my money than the overpriced campus eateries.
Outlet Mall - We have two right now, and I think there are plans for more. They used to be a lot better when I was younger, but now they're not so much discounted, but you can find great deals. My recommendation is to hit them during the week. Weekends are just nuts.
Spanish - if you learn it, it will definitely help. It's not required, because the majority of people speak english. There are a lot of Mexicans (from Mexico) that take trips up here to visit the outlet malls, so if you know a little spanish, it would help.
Housing - I personally dislike the apartments here. There are a few that are good, I suppose, but if you can get into a house, renting or buying, I would highly advise it. I wouldn't go so far as to say that aparments have a monopoly, but my experience hasn't been that great. And that's not just here - I've been mistreated by apartment complexes world wide. But really, unless you just need to get into some place quickly, avoid apartments.
Attitude - It's what I love about this place! Everyone is really laid back and just enjoys life. I rarely come across a person that is just obnoxious. And the drivers here are some of the nicest I've ever seen. Need into a lane, sure, go ahead! Not something I'm accustomed to.
As far as your other items -
There are many churches here, but I don't currently attend one.
What type of gathering spot are you looking for? Weekends are pretty hopping on the square, but it's more of a bar/drinking deal.
I try to walk and bike as much as I can, but it can be a little tricky. Because San Marcos is fairly spread out and hilly, it can be a bit of a chore, but you quickly learn alternate routes that you wouldn't normally take in a car. For example, when I bike home from campus, I cut through Sewell Park. Not something you can do in a car! And if I'm not mistaken, there is a push right now to get more biking into the area.