Veteran of FUT, but new to MUT. Need some help.

Hi there, this is not my first Madden but it is my first time playing MUT. I've been playing FIFA ultimate team for about 3 years, so I know the general concepts. But there's some additional parts I do not understand yet.

-Badges, what do they even do?

-Sets, what's the best way to go about these? Are they worth it? Which ones should I shoot for?

-What are the different game modes?

What should I do with all the shitty bronze players I'm getting at the beginning? Quick sell, auctions, sets?

Should I grind the Solo challenges for a while just to build up good players?

I spent a quick $5 on elite player pack and got Talib. Is buying packs worth it? Which ones?

In simpler terms, I'm looking for a beginners guide lol. Thanks in advance