Well, IME many fish tend to be reclusive during the time they adjust to their new home, Bettas are no different, He should come around, give him some more time. Even after all that you may find out, you have a timid fish that prefers a darker tank. If all else fails add some more hiding places and see if that helps.
My current Betta seems to like the well lit tank, however my previous Betta was entirely the opposite, I actually took out the fluorescent bulb and replaced it with a low watt incandescent to "darken" up the tank.
As far as his appetite, That should return, give him some more time, I had one of my Bettas go a full week before eating.
Note: just read your Sig. Those Gourami may also be factoring into your Bettas "distress" you'll need to watch those two, any signs of aggression they (or the Betta) will need to be moved.