I am in contract to buy a 4unit and do a complete rehab on it.  I'm looking for all the advice you have to offer.  What hvac, paint, toilets you use, what touches you think work, where you buy you cabinets or vanities, value add touches, complete waste of times, special permits to look out for.  Anything you have to say will be useful. 

I followed this hoping to see what people said, but since no one replied I will tell you what I would do... I buy ready to assemble cabinets, vinyl plank flooring, I prefer shower enclosures but at minimum use a tub for savings, and for HVAC I prefer mini splits for heating and AC.

A lot of this is market dependent.