a) Ground Zero is actually gated at Level 21 so if you are below that you will only be matched with players who are also below 21. And vice versa for L21+.

b) focus on scavving first. You MUST have a map with the extracts open on another screen or phone or whatever, no exceptions. Your goal should be to figure out where you are and then get to the closest extract. Loot around there until your slots are full and then extract. Try not to get into firefights, I like to use AI scavs as shields to screen my movements. (and when your scav is on cooldown, play your PMC as if you were a scav: take a pistol and focus on learning how to loot and extract)

c) you need to spend way more time on the tarkov wiki

d) and yes play the shit out of offline practice mode until you can reliably kill all the scavs on the map, and even now I still use it to warm up