I live in southwest Missouri and have a lot of creeks by me. I'm interested in giving the wacky rig a try and am wondering what size worm and hook I should use considering the bass are on the smaller side. I'm thinking a 4" worm with a #2 hook, not sure tho.

My go-to is a 5” Senko or Yum Dinger on a 1/0 octopus circle hook. Considering some of the bigger bass (4-5 lbs) and superdinks I’ve caught with that rig, I’d say bass of all sizes bite it equally well! 

I throw 4" w/a 1/0 weighted hook. The weight is dependent on the current I'm fishing. Fast current, heavier weight, slow current,  lighter weight. Brian.

Dinger4” or zoom finesse worm. If you can, us an O ring. Loose less worms that way and better hookups. You can buy an o ring cylinder and o rings in a lot of fishing departments. Keep in mind, the finesse worms are thinner so you will need to get smaller rings at a hardware store or online. 
for hooks, “1/0 is the biggest I go. Finiesse worms i will go 2 or 4. As mentioned, hook size affects rate of fall, so use accordingly.

 

and yes they catch big ones in streams.