A few issues here. First main one is temperature. Mikrogeophagus ramirezi in any of the varieties (all are the same species) needs warmth, a temperature in the range of 82-86F/28-30C. There are some but not that many species that can manage in this fulltime/longterm. Hyphessobrycon amandae (Ember Tetra) is not one of them. Paracheirodon axelrodi (Cardinal Tetra) and even more its cousin P. simulans (Green or False Neon Tetra) are suited (the common Neon, P. innesi is not), as is Petitella bleheri (Rummynose Tetra) though the latter is a bit active for the rams, especially if spawning is intended. There are some other species OK with the warmth, I could refer to my notes if asked, but the afore-mentioned readily come to mind.
On the rams themselves. A bonded pair can work, or a small group, but I would not consider the 29g tank (assume this is the basic 29g with a length of 30 inches and width 12 inches, correct me if not) sufficient space for the group. As for pairs, the fish must select their mate; any female put in with any male may or, more usually, may not work. If the pair select each other and bond, they should be fine together, though down the road divorce is still a risk. This is not a harem cichlid, so two or three females per male is not generally advisable; if the male should bond with one of the females, they will inevitably spawn and the other females can get a very rough reception, and there is no where near sufficient space here for this not to be a serious life-threatening problem.
As for CO2, this is definitely not a good idea with these fish. They are very demanding of water parameters and conditions being very stable. Everyone here knows I do not recommend CO2 in any tank with fish, but here it is even more of an issue. And my understanding from those who have used CO2 is that DIY units are much more risky for fish. Unloess you want an aquatic garden, there is no reason for adding CO2 in a fish tank; not only the 24/7 respiration of fish, plants and bacteria produce CO2, but more occurs from the breakdown of organics by bacteria in the substrate. I have had to increase surface disturbance to remove CO2 produced during the night in my low-tech planted tanks, as it did affect the fish.