It wouldn't be a terrible idea to move the things around that you have. And it looks like you still have some space in there for more deco, maybe a few plants?
I know many people have kept cories with bettas. But I won't. Let me explain why. :)
I have had cories in a community tank for almost 3 years now, and I've seen a full range of personality. I have had a couple different fish in the tank I have had to remove/ separate from them, because eventually they would get chased and bullied; and even if no physical damage was done to them, after awhile they would end up hiding alot of the time. And I don't know of any cories that should behave that way. When they feel safe and are happy, they are as active, or more so even, than my bettas are; and spend little time at the bottom of the tank. They really only go to the bottom to rest for short periods of time, and to eat. The rest of the time, they are on all levels of the tank.
I tried keeping a dwarf gourami in the tank with them. And once he got settled he staked out the tank for himself; and chased them away from caves, and always from food. I had to put him in his own tank. I also had an SAE with them later, who also started to bully them and chase them away from food. In both circumstances neither bully ever did physical damage. But in a short time of being chased they had to resort to hiding from them, and when it was clear they were unhappy I had to separate the offenders. And after I did so; they went back to their gregarious selves. For reference: http://www.youtube.com/watch?v=4tLL_CpAQu0
I don't say any of this to scare you, merely to warn you to keep an eye on them. It is imperative in a community set up that all inhabitants feel safe and happy, not only because we want them to be; but also because stress can cause them to fall ill. If your betta ends up very chill and ignores them? They will probably be ok. But if he chases them..even if he doesn't do any damage, over time you will find your cories hiding, and this is just not the natural personality I have seen in these delightful little catfish.