Welcome to the forum.
Tankmates: Cory Cats, and Shrimp (some Betta will eat shrimp, though.)..Most say Tetras, personally I don't like Tetras, they nip fins.
Decorations: Any caves that don't have sharp edges, and silk or live plants.
Filter Systems: Aqua-Tech is really good. The Marineland one might be to powerful. If you have a Wal-Mart near you that sells 10 gallon kits, them are awesome.
Food Pellets: I used Wardleys, but I prefer Hikari Bio Gold. I just got New Life Spectrum Betta Formula, going to see how that works.
Bettas: Rose, Sophia, Addie, Ghost, Buster, Holt, Aidan, and Mercutio!
Just my animals: 0.2 Cornsnakes, 0.2 Bearded Dragons, 1.0 Water Dragon, 2.2 Crested Geckos, 1.0 Tiger Salamander, 0.0.1 Tadpole, 0.0.2 Red Eared Slider Turtles, 0.0.1 Map Turtle, 0.0.2 Hermit Crabs, 1.0 Hamster, 1.0 Rabbit, 0.1 Horses, 2.2 Dogs, 0.2 Cats, Chickens, Ducks, Oscar Tank, Planted Bowl, 10 Gallon, 4x 0.5 Gallon, 5 Gallon, and Planted 25 Gallon Tank....Is that it?