What are Archetypes?
Are they just different looks?

Archetypes are preset character templates for both factions. In case you don't feel like customizing, you can simply take one of these Archetypes and play using it.

But if you want more customization, you can take different parts of an archetype (i.e. The Sweat's mask, The Fortress's pants, The Firestarter's top) and mix and match for an even more unique player. You can't mix two parts of the same type together, though (so you can't get The Eel's jacket and mix it with The Bomb's body armor).

Awesome

is there more clothing options or just the archtypes?

There are a few more options available; however, you will only find Archetype gear as outer layer and bottom clothing.

Lots more.

Source on that info, please. Because all I know is, that there are more items. But I figure they rather are "some" than "lots".

Ok now semantics. There are the archetypes and there are additional clothing options.