I wouldn't add anymore cichlids. You have a good number of bolivian rams for your tank size and they will claim all the available territories. Anymore cichlids, and there will be aggression problems when the bolivians start breeding. Bolivians grow very slow but when they are grown they will fill up your tank nicely. At 1.5" they are 6-8 months old.
However, you do have plenty of room for more tetras. For your tank size, you could add 6-8 more tetras. You could add more neons, or a different species that you like. I keep Gold tetra and rummynose tetra with my bolivian rams.
Another option would be to add some small catfish like Cory cats, which could also be kept in a group of 4-6. Goodluck :thumb:
Ed