I just so happens I've kept them 3 times, two different colour forms of thomasi. On the egg test, they wouldn't even develop at 140 ppm, and I had to bring it down around 100 to get fry.
Generally, if the eggs won't develop in a type of water, then the fish is out of its water.
I have one grumpy leftover female thomasi here, if anyone wants to drive up to eastern Canada...
I bred them 10 years ago, then ordered them again 2 years ago, only to have a shipping mishap. 30 years ago I had a group in 140ppm water. They couldn't breed.
@gwand - if I can make a suggestion...mbuna are pretty. But a dive into Tanganyikans may catch your eye. They are no longer as popular as they were, but they are fantastic harder water Cichlids. There are some small species that are beautiful, and not hard to keep. There are pretty Victorians too, but I was unable to keep them as they aren't aggressive - they are downright violent. Tanganyikans, on the other hand, display some fascinating behaviour, and can be in tanks like you are considering. Neoplamprologus marunguensis... very cool.