F2P PVE Crusader Noobie

Howdy. Just hit lvl 47 on my crusader and I'm having a lot of fun! I started actually looking to mechanics and this subreddit.

Can you guys give me any tips for beginners? From what I've read, focus on CR for a long while, but not necessarily equipment. Gems seem crucial (vault, clans, and rifts?). I've seen several lists of all-rounder gems that I want to try and get into.

Any common mistakes to avoid?

Also, if upgrades on legendaries can be transferred freely, I shouldn't feel bad about dumping gold/gems on my legendary gear, right?

Also! Crests seem pretty important. Will those accumulate as I play? I know you can craft them from fading embers, but is there a better way for F2P?

Thanks in advance!