As we all know classes are not really a thing in New World. What is a thing, however, is an established culture of MMOs, and that requires healers, tanks, and the DPS.
Quite a lot of players have used ice gauntlet/musket from the start to end of beta. The build itself is fun to play but unless they fix the swapping bugs (sometimes you just won't swap or you get stuck in a reload animation) it's a little annoying. The nice part of ig/musket is you never need to reload, you can fire, swap to ig, then heavy attack and by the time you swap back to the musket, it's reloaded.
In beta, a musket was really bad against anyone stacking constitution and heavy armor though. You will not out damage any heals from that build.
As for builds, unless a lot of the abilities get buffed on release we would recommend only getting the fire dot ability and maybe trap and just picking up every passive in the sharpshooter tree. Most musket abilities are not worth stopping to reload the gun or going through terrible animations.
For IG you want ice shower, ice storm, and entomb while making sure to get the heavy freeze and critical frost passives in the ice tempest tree.
Again, you will probably notice that your ice gauntlet carries this build. Musket is fun but the damage is pretty bad in comparison.
For release, you're better off planning to carry three weapons, and just using muskets for powder burning at range, then swapping to rapier/ig when they get closer. Just got to make sure nothing is on cooldown or you can't swap.
That is, of course, if you don't have a team that you can trust. Muskets require a good frontline to be able to consistently dish out damage.