And whoever is looking needs to pay attention to big ticket items - electric (is there knob and tube or a big upgrade required), roof, plumbing (sewer inspection with a camera), septic and/or oil tanks, asbestos, is the furnace working, mold, structural integrity.

The roof has leaked extensively and it will likely need to have all new systems (electrical, HVAC, plumbing, flat roof, refurbished steel casement windows, etc) along with significant updates to flooring, walls, bathrooms, kitchens, etc.

Perhaps you can find a “net PM” for 10%, which, in this scenario, would equal a 6% “gross PM.”But I don’t think the numbers really matter in the end, because two potential outcomes appear to me right away:1 - Unless you will have a way into the PM’s maintenace request system or for the tenants to communicate with you directly, you may soon start to have higher vacancy due to tenants who may have leaky plumbing appliances that keep them up at night, tree branches that hit their windows in light breeze, garbage piled up around the dumpster, broken irrigation sprinklers, and the like.

I've been advised to go to at least $250 and preferably $350 unless the plumbing has been redone. 

New A/C ducts and all, new water heater, new plumbing, new kitchen and cabinets, new bathrooms, fresh paint, new floors, new light fixtures, new roof.

To date, the house has been completely re-wired, basement stair covered in order to add 2ft in the bathroom and bedroom #1, all new cabinets, all new appliances, granite countertops, hardwood added into kitchen and bedroom #1, updated plumbing to include drinking water (replaced black pipe with PEX), and currently in the process of renovating the bathroom (wall tile, new fixtures, floor tile).

My investor has been running a highly successful plumbing business in the Philadelphia are afor years.

My investor has been running a highly successful plumbing business in the Philadelphia are afor years.

Does anyone have experience buying a property with a cistern and vault plumbing system?

I really don't know how much all of the big items are going to cost (i.e. roof, plumbing repipe, electrical) and I don't know what is important to fix today and what can be fixed later.