Glad you came to us for help before getting him set up!
A tank that size isn't awful, it will just require a bit more maintenance, and if you get a not-as-energetic fish, he probably won't have any problem with it. However, bettas like very clean water, so in a tank that size, you should probably be doing two 50% water changes a week (no less than one a week) to keep ammonia levels at a minimum.
As for food, Omega One Betta Buffet pellets or NewLife Spectrum are the most recommended here on the forums, since they have the most protein and the least filler (bettas are carnivores, after all!).
You can absolutely add decorations, and you definitely should. Bettas love having places to hide, so make sure you have something that offers some cover. Live plants are the best, but if you get any man-made toys, make sure there aren't any sharp spots on them. As a general rule of thumb, if it will tear pantyhose, it can tear a betta's fins.
As for temperature, you're going to want to get a heater in a house of that temperature. Bettas do best at around 78-82 degrees Fahrenheit. As for what kind of heater to get, that's going to be a bit more difficult, because many of the more affordable ones don't do their job well, either not keeping the water warm enough or keeping it way too hot. Adjustable is best, but I've had success with these:
http://www.amazon.com/Tetra-26447-S...7247&sr=8-1&keywords=submersible+heater+tetra (of course, you'll certainly want to monitor the temperature, at least at first, to make sure your fish is safe and comfortable).
As for cool names, I suggest being inspired by your fish! You want the name to suit him, don't you?