To unlock the final missions, you need 6 of the 8 businesses bought and completed (i.e. a $ icon unlocked at their locations...in addition to the $ icon unlocked at the mansion). Whether you have the remaining 2 businesses bought/completed is irrelevant to the storyline. However, the Printworks business MUST be one of the 6 completed (printing money is part of the storyline).
Non-completion of the Malibu business would make Phil's optional thread unavailable, tho (completion of that one lets you purchase heavy weapons from his cache). So it might be in your best interest to do that one as one of your 6.
BTW to earn a LOT of money quickly, you can use the "Cone Crazy" mission (drive a Stallion to the top of the carpark near Raphael's). Wait until the last second before collecting the last checkpoint each successive run. Since the purse doubles after each completion, it's no challenge at all to get as much cash as you need.
Or, you can take advantage of the "level 12" Vigilante exploit. Upon reaching level 12 when wiping out criminals, 3 of their vehicles will continue to spawn at the same location chosen last time (the 4th will frequently spawn at an invalid location and "self destruct"). If you have access to a Hunter helicopter, this makes the mission a cakewalk...you can just hold down the rail gun button to blow away level-after-level of perps. Works best if you can force level 12 to spawn inside the closed-off airport area.