SA isn't as humid as Dallas, but it is very "burn your skin like bacon" type of heat. I lived in Wichita Falls for a year and a half and I'll take that humidity over the scorching heat of south texas all day, any day. Though SA isn't as scorching as where I'm from (Laredo, about 150 miles south of SA).
As far as the city, it's a really nice place to live other than the heat. I lived there for about a year and I liked it. Lots of stuff to do. Not sure on the schools (I went to UTSA and it's a really good university but I assume you're talking about high school and below?), and just like any other city there's some "Clean" parts and some "not so clean" parts. Crime rate depends on where you live in the city. When you find about 5-6 places you might want to live do some research on the crime rate of those areas before making your decision IMO. That info should be available online or from the SAPD.