You will need more than one oto in a tank - they seem to be unhealthy by themselves. Depending on how aggressive your betta is, shoaling fish can make him harass oto's and raspboras (dont worry too much about this unless he is overly aggressive).
Adding shrimp especially RCS's, your going to need alot of hiding places and foliage for them to keep away from the Betta. Once again, if the betta is overly aggressive - I highly recommend you dont stock it with shrimp. You also wont see your shrimp when lights are on because of the betta
Ghost shrimp - why ghost? look into Amano, a bit bigger but they are heavy algae cleaners.
I know nothing about raspboras besides they are shoaling fish but maybe think about just sticking with oto's, shrimp and a betta? oto's are very active and lively when they have 5 or more.