check out flip aquatics or LRB aquatics, they have USA bred shrimp. all of Lucas' shrimp are bred in his house and Flip aquatics has home bred or imports available but quarantines them thoroughly.
i haven't personally ordered any shrimp online, but those would be the ones i would go with if i did. i watch their you tube videos and would take comfort in seeing exactly where the shrimp are bred/ raised.
as to how many you should get, i would just start with one group (lots of the ones I've seen online sell in batches of 10). shrimp breed relatively fast so if youre patient you'll have tons before you know it. i started with 10 blue dreams and now have hundreds so i had to give lots of them away. i bought 8 crystal reds in november and now i have like 3x that amount in babies. my thinking is: don't buy the max amount your tank can handle, just get enough to breed and let nature take its course.
you should definitely make sure your water parameters can support the shrimp you want, but if something goes wrong its better to make a mistake on a few rather than a lot.