I have to disagree on the snails-as-cleaners thing. They are ok for soft brown algae, but that's easy to clean yourself. They do diddly-squat for hard algae and prefer to just snarf up food that the fish didn't eat. For such a small tank, I'd go with either a nerite snail or no snail.
Then again, I freely admit I am biased against snails.
Rather than buy a bunch of shrimp at once, I would start with just three. If they are still ok after a month or so, build up the numbers. :)
Make sure you don't add everything at once and cycle beforehand. :)