Agreed with Pufferpunk.
I have a small N. wennerae. He's the bomb.
But if you like species that like to come out more get a peacock. If you get a small one you could probably wait a few molts before you had to upgrade size but yeah...
Get a "long" tank because they tend to stay near the bottom and don't need that much vertical swimming area (if it's a peacock mantis 5-7 times the height of the shrimp should be fine)
A skimmer might not be needed. Buy one if you want to spoil him...
Depending on your individual, you might be able to feed him FD stuff. But if he's picky you're gonna have to find him live crabs, hermits, snails, crayfish. ghost shrimp. You get the jist.
Peacock and larger smashers:
Deep sand (or a PVC tube)
Larger tank and hard shelled foods
Spearers like P. ciliata:
10gal is comfortable
Soft bodied prey like fish
Smaller Smashers:
Same 10gal tank
PVC tube for hiding
Smashable prey (like freshwater snails, sw snails are too thick shelled)