I am not saying that plants are all bad, I just would not use live ones. There aren't a whole lot of places where you can pick up plants and not end up with snails or other pests. It certainly does not hurt anything to use fake ones.
Also, your tank will be fine but tubs make things a bit easier. You can still use a divider, most people make their own out of some platic craft sheet stuff. Plus, when you are dealing with only 4" of water, keeping the lid on helps you keep up humidity and helps to keep your temps from fluctuating. The humidity does need to be kept up a bit, since bettas are still labyrinth fish and need the humidity to help them grow their labyrinth organs.
P.S. I have bred bettas and gouramis in the past using these methods, I also know what works for me and what has worked for many others. Maybe it would be best for both of us not to assume that we know it all and meet somewhere in the middle. After all the point here is to try and help the OP.