I wouldn't get a clown loach. They prefer to be in schools, and while it may take years, they will eventually outgrow even a 55 gallon. How about yo yo loaches instead? I really like mine, and they will stay small enough. I wouldn't add a male betta, but a female would be ok. JMO, but I would think that the flowing fins of the male would be too much temptation for barbs. A school of corys would be fun. A school of rainbows would add a lot of color. A severum would do fine with barbs, if you want to take things in a little more aggressive direction, and Bolivian rams would work if you didn't. You really have a lot of options here, and I think you're going to have fun choosing!