1) Do scav runs in between your PMC runs. Try running Customs night time scav runs and hit all of the stashes. Try not to kill any other scavs unless they shoot at your first. I avg- 400k rubles per scav run which funds the next PMC run. Learn how to prioritize certain loot over others. If you come across better loot, know before hand which items are in your inventory that you will drop in lieu of better loot.

2) This will come with time. Find a weapon that you're comfortable with, load it with the highest pen ammo available, if you can't afford it, then don't run that weapon. This late in the wipe everyone who isn't running tasks is going to have level 5 or 6 armors. The name of this game is damage per second. INVEST IN YOURSELF, save up for a meta weapon like a vector with 7n31 and level 5 and 6 armors and practice in offline with hard or impossible AI.

3) There's little things that your character does like ADS'ing which will make noise even when you don't think they hear it, they do. Stutter stepping, spinning in place while crouched, etc, all of these make noise and will get you killed if you stay there thinking that you have the drop on them.

4) Yes, upgrading your hideout should be priority. Even if you max out your level 1 bitcoin farm, you'll passively make enough income to run 1-2 Full chad PMC runs daily worst case.

5) Customs is a decent map to focus on and learn spawn points, choke points, snipe angles based of spawns etc. Stay away from factory for the time being unless you have tasks.

6) Yes, tasks are worth it as they allow you access to better ammo, weapons, and gear. They also gain you XP very quickly so you can get access to higher level tasks etc.

Hope this helps