I like this one.3) Highest risk because too much carrying costs with hard money, inability to predict where market will be when it's time to sell (9 months + modular construction time), opportunity cost if your funds are tied up and another deal comes along so I'm not a fan, negative cashflow like crazy over a long period of time is no bueno.Like the numbers on your deal, too bad 9 months + build time is really far out.

If its the main house,can the seller do an owner carry with a subject to (if they have a loan) for a few months while you complete the remodel?  

You probably wouldn't want to use direct vented gas fired hot water heaters since they carry a bigger price tag, so if you use gas for hot water heating without direct venting your exhaust has to go through the chimney - there are sizing requirements for that and requirements for how to share a chimney; electric hot water heating won't have this issue.Then you have PECO to install gas lines and meters.

You can carry the losses forward and apply them towards your 2018 taxes.

Note the lath stuck up in the cavities from previous repairs: the guys that rigged the last repair job didn't even carry that out.

You can have the seller carry back part of the down payment or bring in a private lender for part of the down payment. 

Partnership agreements carry significant weight unless they violate some sort of public policy or seek to waive a duty case law demands is non waivable.

Owner financing really comes into play on a 5 unit or more because then someone is going to have to carry a commercial loan which is much harder to get. 2-4 families get snatched up quick.

We did not make it inside before she stopped twice to carry on conversations.

The the sellers may have capital gains income from the sale so by recommending they carry back a note with you, they can spread their gain out over a multi-year.