Bettas aren't a very good community fish. Some people have success, but many don't, so unless you have another tank for him incase something comes up, I'd suggest you avoid it.
I would get more tetras. In my opinion, they look better in larger groups.
Also, cories and plecos are great bottom feeder fish. I think the best pleco for a 29 gallon is a bristlenose, because they stay small.
I would do this:
10 tetras (my suggestion is cardinals or black phantom tetras)
4 platies (or 4 swordtails)
6 cories (pandas are my favorite)
1 bristlenose pleco
I also think you could add one more group of small fish, such as marbled hatchetfish.