Hi
The worm is most likely planaria. A small harmless creature stays small you can do a quick google search for more info
I havent kept a betta before so wouldn't know. If you do get a betta is it possible to move the tank to shade maybe? :dunno:
I quite like the new layout :thup: once the plants grow a bit you can always change it if you want.
In conclusion looking good, should see the mess my turtle made of the plants I put in his tank :slfg: