If you're a new player, then you probably can't play raids because those will require maxed 5s to complete (because they're pretty tough) You can start PvP any time you want, but if you want to climb the ranks you'll need a good 5/6* team.

Free Renji is awful because he has bad stats, bad moveset and a terrible special. And we are all tired of him lol

2x gachas are the best to pull from, and the top tier characters right now are Dangai Ichigo, both Kenpachis, Haizen, Barragan, Shunsui and more (there's a tier list here on Reddit, use the search option and you'll find it because I'm too lazy to link it)

Premium is bad because it contains all non seasonal characters released ever so there's extremely low odds of getting who you want.

No difference between multis and solos, up to you to find out which one works better for you.

Beginners Pack is definitely worth buying. Buy it!

6* are stronger than 5, and also a pain in the ass to evolve (but a good character is worth it). You first need to have good 5 to get you through the story and play coop and raids before evolving 6. And 6 take time to max out and when you evolve a 5* to 6* they revert back to level 1 with 0% soul tree so pretty much unplayable.

I'd advice you to have at least 1 strong 5* from each attribute before making another character a 6*.

Hope I helped!