you pretty much described what i plan on doing with my 20g tank.
i plan on having driftwood with christmas moss attached to it, i want some rocks and maybe put a different kind of moss on them, also my tank will be planted.
I do plan on having fish, snails and shrimps with mine.
as for fish i am ordering some Celestial Pearl Danios, my snails would be Malaysian Trumpet Snails, shrimps would be bamboo or Carribean filter shrimp (if i can find one), i will also have Red cherry shrimps.
my plan is after i get my cycling out of the way i will get my RCS and MTS put in and make sure my RCS are breeding. then i'll bring in my CPDs.
CPDs might eat some of my baby shrimps but at least i know my shrimps will breed and still thrive. so mainly you can have all three but you just gotta do some research