In a 29g I would only breed one pair, it'll be less stressful on the parents. I recommend at least a 48" footprint for two pairs.
Also for filtration you will have to weigh the options yourself. Canisters are more efficient and they are pretty much unbeaten in media storage. But they tend to cost more and can be complicated for a beginner to operate.
HOB filters are simple to run, cheap, and do a decent job at filtering. But they can be noisy, HOBs don't have the media storage capacity a cannister does, and tend to wear out faster.
Do your research on which would better suit your needs. Personally I would run a HOB on a 29g tank and if you have just the rams in there. Shoot for a filter rated for a 40g tank. Maybe a Penguin 200, or a Emperor 280.