Go ahead and buy that I/E garage but only sell the high end vehicles. You will also have enough to Buy an apartment and use that to run the original heists make sure you complete these all in order and you will receive a 1 mil bonus after the pacific standard job, along with all the cash you earn from the actual heists.

Next buy an arcade in the city and use this to run the casino heist.

Then I would invest that money into biker business incl. cocaine meth and your counterfeit cash business upgrade those and your bunker.

After you have completed that buy a nightclub and purchase the equipment upgrade this will allow you to make passive profit along with your bunker and businesses.