Once you start to learn what items are worth looting / valuable on scav runs and your PMC hits level 5 the game opens up an awful lot because you get access to the Flea Market. It's a player market place where you can buy and sell anything and will give you access to items traders won't sell you. My PMC is only level 18/19 as I haven't put a lot of hours into this wipe yet I'm running around with class 5 armour and end-game ammo because I've made good money from the scav runs I have done.
Ammo and armour will be the biggest blocker you face as a newer player. Class 5 armour against the ammunition you have ready access to you might as well bang your head against the wall. You will lose a lot of gunfights and it will be frustrating, but as you learn where (and equally as important, how) to move around the maps you'll learn to read situations better, you'll recognise which gunshots belong to which weapons, when to rush in head first, when to sit back and let a gunfight play out before swooping in. Tactically the game is unrivalled in my opinion. But you'll always come across thiccbois who run around willy-nilly with the best armour available and sponge rounds because their aim is on point and they can afford to be aggressive/reckless. One well placed shot can take down anyone on 99% of scenarios though (again, ammo dependent).
Your first few missions will be centered around the Customs map so that's a good one to learn. Most higher level players sit predominantly on the Reserve map at the moment as the loot is far better there, so you shouldn't come across too many challenges. There are also certain characteristics of the game you need to adapt to - for example if you're not wearing armour, or very low rates armour, and you start shooting a scav but fail to kill him, if he's fired rounds at you already don't re-peak the same corner as he'll be zeroed in on your face and you'll likely die.
Can definitely recommend DeadlySlob's videos and streams, he's a very likeable character with an upbeat personality. Kotton is very marmite and most people don't like his meme/toxic-centered humour. Klean is a very good player that plays the game how I would expect it to be played - he clears his sectors and methodically moves through the map. Some people get put off his stream as he seems a bit hateful, for lack of a better word, towards viewers but again that's just his humour - he's a very knowledgeable bloke about the game as he used to be one of the community moderators and is constantly talking to the lead dev. People like Pestily and GhostFreak I avoid watching for the most part - they're playstyle isn't to my taste, and whilst they're both very adept at the game, I think it takes away what the game tries to promote - they're hyper aggressive players that use the full range of what's available to them; GhostFreak is renowned for using a thermal scope to scan huge swathes of maps for targets before rushing headlong towards them and blasting them away without the other person having a clue what's going on. Makes for entertaining watching at times but he makes it seem far easier than it actually is.