2.5Gallon seems a little too small if you want to populate them. Having a 10 gallon is a good starting point. There, you can really try different things, such as layout, plants and the water quality.
I would say you can try a 20 gallon long for the best result. It is large and spacious for anything you really want. If you want to breed, then you should follow that King fisher said. If you just want to have a nice looking shrimps, you might want to invest in couple items that could help the shrimp quality. substrate, food, lighting, driftwood, and water quality.
Overall, just try it out, it is really fun and RCS are not too hard to keep alive and breed.