As for companions, my only caution would be that you watch your little guy carefully. Bettas are usually the recipient of aggression and not the aggressor himself!

There is a compatibility chart link below that will give you some help on who makes good friends for Bettas. Angelfish, 1 swordfish per tank, neon tetras (avoid the lamp-eye tetra . . . too nippy and will eat Betta tails!), Cory varieties, Barb varieties, and some catfish. Make sure to avoid cool water fish like goldfish. Also avoid the gouramis since they are cousins with the Betta and may fight. Tetras, specifically, are schooling fish so add about 5-7 of them and they will do better. Once you add friends, be sure that you are around for at least a day or so to observe things and make sure that everyone is getting along!
On the plants, JAVA MOSS is a great choice since it helps decrease ammonia and nitrIte levels in tanks. Most local pet shops don't stock it, so you can purchase it from a place called Aquarium Garden online. Water lily is another good one that my Bettas love to hide in! Neither one require anything special to make them grow either!
Hope this helps!