Cherry shrimp are great, nice and colorfull and do well on algae and will help cleaning up small bits of food the fish spit out. www.aquabid.com
has people selling them for a decent price, even with shipping it tends to save alot of money over fish stores.
First ya need to get rid of the dwarf frogs though.
Most LFS's take fish back for in-store credit, and you can always take them to another store if the one you baught them from won't. Even if they won't give ya money, it's not fair for the fish to be housed in an enviroment outside of what it needs, please re-home the little guy. :)
Missed the question about stocking levels, sorry.
I've read of people doing 60 or so in a 10 gal when breeding for food, I'm sure they did very frequent water changes though. A safe bet would be 15-20 shrimp with no other fish, or 5-6 with fish, so with 6 shrimp you could do 8 or so neons or fish that don't grow over an inch.
You'll be needing to do bi-weekly or weekly water changes totaling around 50% with that level of stocking, and you'll also want decent filtration, something with a biowheel like a penguin rated for 20-30 gallons.
I personally use Emporer 280's on our 10 gallon tanks, it's a little over kill but my water is always crystal clear with no ammonia or nitrites.