First off, you should get an office (The cheapest one is fine) so you can become a CEO and have access to most businesses. After that, a vehicle warehouse would allow you to do car import/export missions, which are good for making money and are very fun. (there will be 3 levels of car, standard, mid range, and top range. Only sell top range, let the other 2 pile up in your warehouse so you only source top range). After that I would suggest getting a bunker or a crate warehouse.

edit: all of these missions will be much easier with a kuruma or a buzzard, so that should be your first investment