If it were me I would put the glofish in the 55 because the 5 is actually to small for them and then I would put the betta in the 5 they are from my observations normally more active and happier when they are kept alone. If you like you could put a mystery snail in there they are neat to watch and most of my bettas ignore them and it would take care of any food the betta may miss. I think I answered everything if I missed something just pm and I will answer it. Also I would like to suggest that if you plan on doing real plants give him something that floats like duckweed, or brazilian pennywort my guys love there floating plants. Sorry I had to do this in two part because it was to long and for some reason I can not pm you.
Your Ph is fine as far as what you can and can't put with him in part depends on him. Some bettas are super aggresive and can only be by themselves others do well in a community tank. You can get some idea by floating him in a bag and seeing if he flares at his tank mates even if he does not still watch them real close for the first few days. Do not put any other anabantids (air breathing fish species) such as Gourami because they will fight. Do not put anything that is know to nip fins like tiger barbs because they will tear up his fins and stress him out.