Need help for early game

I am currently still struggling alot and was wondering what else do I do other then getting exp for progression? I also have a list of questions that I need to be answered - Thank you

Armor choice - Don't know whether I should choose to wear gold or diamond armor as I've seen the great benefits of gold armor like osmosis, 50% damage gold weapons, etc. but I don't know whether it will "protect" me as much as Diamond armor tho.

Exp Priority - I don't know whether i should prioritize exp for my disenchantment table, L menu or just keep it prioritized to my attack and agility for a crossbow so I can create a crossbow and kill a dragon?

scarlite reaver, my fav weapon - I currently am trying to find a way to get a black heart from a shambler but my defiled lands biomes is trash and only spawns lycanites mobs and also has like 20 puddles of purple liquid So is there any better way to get a black heart other than those steroid versions of shamblers in the mines or just a way to promote them to spawn in the MOST dangerous place to go to in night time without dying?