I keep mine in a 6.6G and 12G Edge tanks, also kept some small ones in a 2.5G, but not for breeding.
A basic 10G would work great I think, for breeding.
I think that a tank that would be cycled and stable, in other words, mature, for a 5G. Otherwise you are likely to have water problems and maybe dead shrimp.
It would depend on the size of the start up colony like 10 shrimp (5G) vs. 50 (10G).
If you are wanting to breed you will likely need to cull. So you will need to also decide if you need another tank for the less than ideal ones, the culls (unless you have pretty small fish in a tank already to keep them with), or what your plans are for them.