I set mine for 26 degrees Celsius not sure what that is in fahrenheit.
Regarding plants - you can have as many as you want, do you know what kind of look you want to go for? Just make sure there are plenty of open spaces to swim as well as hiding spots too!
Thickness of the substrate depends on what type you are planning on using, I would put anything between an inch to 3 inches (thicker at the back of the tank to make it more aesthetically pleasing!) but anything more than that is likely to get a bigger build up of harmful gas pockets.
Make sure you wash the substrate very very throughly! As if not you will have all sorts of bits floating around and your tank will be very cloudy for ages.