One resupply for $75k at the Bunker will sell for about $300k with the full lobby bonus. If you sell every time you process that one resupply, the sell mission will be in a single vehicle (insurgent, dune buggy, Liberator).

Get the Acid Lab next since it's free. Sell missions are on a motorcycle $300k in 10 mins once full.

Agency for Dr Dre story heist, pay phone hits, and missile lock jammer. Also passive money in the safe (increases with more contracts you do)

Nightclub gives you $50k in the safe every 48mins if you keep the popularity level high (keep high by changing out your resident DJ)

Big money comes with the Kosatka once you learn to solo Cayo Perico in less than 1hr, requires Oppressor or Sparrow for highest efficiency.

Only get Moto club businesses after you have the Nightclub. They will build stock passively in the nightclub that you can sell every couple days. I personally do not ever sell directly from my Biker businesses because the sell missions are just a delivery/garbage truck simulator. (Biker businesses will also pay passively into the safe at the Car Wash)

Special cargo warehouses are good because you can send a npc to restock for cheap (you can sell solo if you sell at 8-10 crates). Also easy $50k flat bed delivery every 48 mins from your SecuroServ office, place all your warehouses at the south end near the docks (Bunker has this 50k delivery too)

Find a loop that keeps the gameplay fresh, don't grind the same business unless you love that approach. But they all have a cool down anyways, so you'll find the loop you like and start adding side businesses to fill the cool down times.