I'll try to answer some of your questions. Fishnut2 would be more knowledgeable, but I'll see what I can do.
First, what is your pH? It's generally better to acclimate the fish to your existing water conditions. Adding chemicals to the water is best avoided if possible as it's difficult to maintain and who needs to buy more stuff?
My pH is actually pretty high and my cories do very well, spawning on a pretty regular basis.
I don't know this for sure, but seems they wouldn't want a river. Most tanks aren't going to present a problem, I'd think.
Males tend to be smaller and less "plump". Generally pretty hard to sex them. If you want to breed them, it's a good idea to have 3 males to 1 female.
I don't know about light. But I don't think any fish likes total blinding light. They rely on smell for food more than sight, so I don't think they'd object to a lower light tank.
I'm unfamiliar with shrimp in aquariums. Would think they should be fine, but researching it is always a good idea.
MTS should be pretty easy to get most anywhere. Some lfs give them away. Check aquabid or do a search on Google for snails and there are many places to buy them online.
What you see corys doing when they look to be sucking on plants, they are looking for food. Generally their little mouths and whiskers are always in motion.
Hope this helps.
Check out
www.planetcatfish.com for good info on all sorts of cories with lots of pictures for identifying them.