Assigning Retainers

[Enkidoh]

Welcome to Eorzea!

Whichever class you assign to your retainers is up to you, however the class they are set with will only gain exp up to whatever level you yourself have in that class (for instance, your character information says you are a level 34 CNJ - hence if you set your retainer as a CNJ then they will only level up to 34 until you yourself exceed that level. Accordingly if you set a class to your retainer that you have never levelled and is still at level 1 on our main character, then that retainer will also be frozen at level 1 in that class forever and never gain exp). So be mindful of this.

As for setting a Job, you can set a Job to your retainer when they reach level 30, but it doesn't seem to affect their ability to bring back better items (it's mostly just handy for being able to equip high level Job-only gear like Artifact Armour that they can't equip as a class). I'm not sure what you mean by 'skin' as that term is not used here in FFXIV though.

This page has more information on retainers and the retainer venture system.