How many ghost shrimp can i have in my 20 gallon tank?

How often will the reproduce?
How do i stop the brine from being sucked up in the filter other then java moss and a sponge on the intake?
what kind of hiding spaces do they like for breeding?

Size 20 Gallon

sub strait: Subsoil, topsoil, peat moss and gravel.
all live plants:(DIY C02) java moss, Green Jungle (Vallisneria sp.), Corkscrew Vallisneria (Vallisneria torta) and Cabomba Green (Cabomba carolina).

Inhabitants:

10 ghost shrimp(not sure how many i can have - advice welcomed.)
2 guppies.
Daphnia