Try looking at:The Best Types of Markets for Profitable Turnkey PropertiesandWhat to Ask When Working With a Turnkey Provider

Everything after that is profit.....? 

You can do it yourself and reap the profit.

This way, your partner and you are splitting profits through the company.

Time is money, even though you might make a great profit with a gut rehab they tend to take a lot longer.2.

Show separately for 2017 and the 3 preceding years: gross sales, cost of goods sold, gross profit, percentage of gross profit to gross sales, amounts collected, and gross profit on amounts collected.It seems, after reading this, that your solution would be the correct one - enter the gross profit for each year on Line 1 of Schedule C with a separate statement attached to the return describing the installment sale and how you arrived at the gross profit. 

***My goal is to use profits from flipping, to invest into multifamily and then scale up from there. 

Once the house is sold, the lien will be taken care of and the seller will walk away with a profit. 

There are two ways to do it.If you are looking to buy as a primary residence, you base the value on the comps with any adjustments for condition and amenities.If you are buying to flip, you use the flip formula: ARV - profit margin - rehab costs - closing costs - finance carrying costs = maximum possible offer.If a seller is holding out for price, a low offer without contingencies doesn't mean very much to them.

My understanding is that it is very common to have negative cash flow and to speculate on appreciation to profit.