My parents were both from Seguin, and both lived there until they passed away a couple of years ago.
I'll do my best to answer your questions.
1) There are a LOT of Hispanics there. 30 years ago it was about 1/3 White, 1/3 Black and 1/3 Hispanic. It is now probably 60-70% Hispanic, about 10% Black and 20% White. There is a large illegal immigrant population. I have heard stories of gang activity, but no more than many other places in South Texas. That said, it is a cool little town with a town square with a county courthouse. Definitely a small town feel. It is also a bedroom community of San Antonio - a lot of people commute the 40 miles.
2) Texas has Castle doctrine and stand your ground. Quite gun friendly. Recent (Jan 1) approval of open carry if you have CHL. They also made CHL much easier to get (6 instead of 10 hour class)...renewals by mail without a new class.
3) OK to carry in vehicle without permit - considered an extension of your home.
4) I don't know of a range with distances like that. That's just because I have never been involved/interested in that. Most I have seen go up to 300 yards. I'll leave that to others to respond.
5) I'm going to answer that "probably"., but it's going to be a ways away - probably well West of San Antonio.
Seguin is a pretty nice little town. They have a beautiful public park (Max Starcke Park) and the Guadalupe River flows through it. Be aware that areas flood! Some gorgeous homes on the river though. Close to some of the best barbeque in Texas too.
Having spent a lot of time there though, I'd consider looking at some other towns like New Braunfels (pop. about 55,000) - 12 miles from Seguin. Lots of tourists in the summer to tube the rivers and a Schlitterbahn water park. A great little town though. New Braunfels also has the shortest river in the world - the Comal - 1 mile from mouth to source. Another would be San Marcos (also about 55,000) probably 15 miles away). Lots of college students (Texas State University) - considered one of the most beautiful campuses in the US. With all the plusses and minuses that a lot of college students bring. Not many good restaurants in Seguin (not a lot of variety) - LOTS of good restaurants in both the other towns mentioned.
PM me if you want to talk - I can give you a lot more detail!
Jim