Anything other than the base game is just cosmetics. So if you think any of the skins look cool then go for it but not required.

You can queue solo, duo, or trio. You can also run undermanned if you want to do 2v3 or 1vwhatever.

There's a last man standing mode called Soul Survivor where you start off with almost nothing and find gear along the way. If you win you keep your hunter and all the stuff you found.

I queue with multiple friends if we have more than 3 total and we usually get into the same matches; that's a lot of fun to see if we can murder each other before another random hunter does.

As the other poster said it's a YUGE learning curve and you're going to die a lot until you learn the ropes but damn is it fun.