I would continue doing as your doing (maybe bump up the dosage if you can) and if there's been no change in another two to three days try a different test kit and test again. Seems a bit strange they haven't moved at all in three days of dosing bacteria.So how long should it take for the nitrites to come down, been using stability for 3 days but they haven't budged.
My tank is just about ready, any thoughts on what fish to put in. I thought about a couple snails, a hermit crab and 2 yellow tail damsels
If you add damsels now, chances are you won't be able to add any other fish. Damsels usually don't play well so any fish you add afterwards may be killed. There are always exceptions to the rule, but as a generalisation damsels are not a great idea.
Also, you'll need quite a few snails and a few hermits too, especially of you like to feed heavily
That list mentioned above is good, again I would forget damsels for now though.