They will nibble at the plant, but more likely to only graze on algae, just because they're starving. Male Bettas cannot be kept with another male Betta. Some fish, notably barbs and cichlids, will be a little aggressive and prone to fin nipping. More docile fish like the small tetras, danios, guppies, platys, swordtails and the various corydoras catfish all get along well with Bettas. Males are far more colorful and in the aquarium varieties available have have long fins.
Females are less colorful and they have shorter fins.
About 5 years is the life expectancy for a betta. Much depends upon how old the Betta was when you got him. Buy a book or two about Bettas, read all of the literature that you can, and join a Betta club or two. Books you can buy about keeping and breeding Bettas can be found at Bettas or at our bookstore . Then you will have the information, reliable resources and sources for a good genetic stock to begin.