So the requirements are that you need to have atleast:
A vehicle warehouse ofcourse and a office
10 standard range cars with no duplicates
10 mid range cars with no duplicates

So you need to gather 10 standard range cars and 10 mid range cars with no duplicates after doing that you will only get top range cars no matter what happens but if you sell your standart or mid range cars then you can get again cars that are not top range but if you don't then you will only get top range cars

The requirements for gathering cars the most effective way are:
A cargobob doesn't matter if its the military one or jetsam their the same anyways (jetsam is uglier)
An office and a vehicle warehouse

Now after you source your vehicle from your computer in your office get to your assistant and order
cargobob it costs 200$ to order him which for gta standards it nothing indeed you will directly fly of your office roof with your cargobob get to the vehicle location either instantly get your car with the cargobob or land and do whatever you need to do to get the car to the cargobob that depends on the mission you were given like if the car is just parked somewhere you can just lift it up but if it isnt like when you first need to kill some warboss then kill the ♥♥♥♥♥♥♥ warboss then get the car drive it forward where your cargobob can get it then get your cargobob and then the car with your cargobob then just deliver it to your vehicle office crookstar even added a special animation when you deliver your car with an cargobob just get the car on the same elevation as the roof of your warehouse and the animation triggers and your car has been delivered this is the most effective way of gathering cars.

After gathering your beatifull top range cars ofcourse you will want to sell them to get money so you can sell also only 1 car if its just you but the more associates you have the better and the more cars you can sell at once always select to sell it to an specialist dealer so you get more money the only negative point there is that there is a risk that when this car gets destroyed that you will lose 20k for nothing but if you don't then you will win 80k for every top range car if you neither damage it upon gathering and selling ofcourse so when you start selling go yourself and also tell all your associates to go off rader by calling lester its much cheaper but it only last one minute where ghost organization last much longer but costs a lot of money so in the most time you will not be able to deliver your cars in 1 minute but it doesn't matter because until other players realize then you will be already off but when there is a hydra griefer then go ghost orgazation because it still better paying for that then losing all your cars and then losing a lot of brain cells because you lose them also because of anger and just like that money in gta was this detailed enough? ofcourse it was.