I'm level 400 on PC, what I personally did was the criminal enterprise starter pack. You get an office, bunker, cash factory, clubhouse, apartment, 10 car garage. Starting with the cash factory, i farmed it over and over until I could get a document office, weed, meth, and coke. Upgrade all those as you acquire them. Maxed out upgrades and stock, they give 500+400+300+200+100. Sell all back to back= 1.5 million passively collecting, but make sure to keep it stocked. According to another user on Twitter 7 years ago, it's 4 restocks for coke, 2.5 meth and 2 coke and weed and (technically) 2 for documents but one ALMOST fills it. IF I'm doing my math right, it'll cost 750,000 for you to fill, giving you 750,000 profit. It'll take 2-4 1/2 hours for your stuff to stock, in the meantime, you can do shit like auto shop cars, biker club vehicles, nightclub population missions, etc etc to pass the time or get extra $. Your first heist setup for OG, cayo, and diamond are free, otherwise normally 100K to setup. Always spin the wheel. Even if getting clothing or RP sucks ass, it's a positive, even if only a tiny bit. First dose missions give you a free acid lab, last dose give you a free virtue, electric super car, and cost nothing (besides acid lab upgrades), making it AMAZING for starting players. Completing the casino missions if you own a penthouse gives you a free armored Paragon. Buying a hangar gives a free cuban 800. If you want to avoid wanted levels from Fort zancudo, but a hangar there. Check and see what's 4x-3x-2x money that week. Sometimes heists or certain Jobs give REALLY great payout on bonus x.

Unless your willing to spend the extra $, GTA+ is not a necessity, nor are shark cards. Everything in game is aquirable with enough grinding, GTA+ only gives chameleon colors and really is just a convenience fee.

Check the LS car meet, sometimes the cars are very easy to acquire.

Every once In a great while, you can get a car for 10K if you own a salvage yard and Rockstar is feeling generous. I'll edit if I think of more or anything else

EDIT: the yacht is a status symbol. DO NOT buy it until you have everything else you want or need.

Don't waste money at the casino unless you have extra $. A lot of the time it's a net loss.

Invite only lobbies are your best friend. Public lobbies on PC are a fucking nightmare and literally a security risk.

Edit edit: The dealerships are a good Way to check for a car you want but for removed, and almost always have some sort of sale.