That's about right if I had to make an educated guess. The filters won't be established with bacteria nor will the tank for a while but going easy on the number of sand shrimp to stat will give things a chance to build up.

Oh and don't leave the tank empty with nothing in it. The bacteria will die quickly once their food sources run out. A water change and replacing sand will help again but will cut down on the number of SS you can keep again.

I iamgine once oyu get a 50 gallon tank established it could support 50-75 shrimp fairly easily.