Nothing wrong with that size of a tank for a betta, that is a palace! lol..
The things you want to remember though with using larger tanks, is that some male bettas can have a hard time swimming in larger spaces, at first, until they build up their muscles. Most live their lives prior to you picking them up at a store in half gallons or less. So you will want to make sure your filter is on the lowest setting, or
baffled by that way, or using another aquarium sponge in the outflow to help cause less of a current. But in that size of a tank, it shouldn't be too big of a problem as long as he has a lot of surface space that isn't being moved around. You will want to make sure that it is densely planted with medium to tall plants and a hiding spot or two such as a cave. It will help keep his stress levels down some from being in a larger tank.
A tank that size he would be good with other peaceful fish, a group of 5-6 cory cats would be awesome cleaners, and since they are bottom dwellers, your betta won't have an issue with them. Platties, female mollies, guppies are good with them. A tank that size you shouldn't have a problem with the smaller grouping fish such as the different tetras as they are usually mid level. Sometimes in smaller tanks, the small fast fish can fluster and stress out a betta, but a larger tank like that I would imagine they will be fine. But adding in tank mates is your choice, of course =) Just make sure they are mid-lower level swimmers, because others, like gurami's are top dwelling and territorial and will fight with your betta. They are bullies
You could also consider doing a
DIY dividers and have quite a few in there. Just make sure there is a few inches from the water level to the top of the divider so they won't jump over.
As far as the Nano goes.. I think a member on here has one for his, but other then that, I have no personal knowledge of them.