Probably best to get an addendum added to the contract early in the negotiations for this one.

Most likely homeowner wnt mind not a big deal to ask for a drop the equivalent to your added fees

My worry here is the long amount of time I'd have to carry this extra debt, and that it might sour an otherwise good deal with this payment on top of a commercial loan. 

We've got the data and are in the process of adding it to our user interface.

But if you need the time to prepare anyway would the added stress be worth the rush of trying to sell now?

But when I look at properties now it’s hard to find anything that makes over $100 a door unless it’s a D class.

Adding a master bath is going to drive the appraisal value. 

Lets say we put in 200 hours of time (probably spent more) and my time is worth just a lousy 10 bucks an hour, that is a $2,000 extra loss right there.

There's no exact science to it but like you said it's only usable about half the year (due to temperature, I presume) and then even when the weather is warm, it could be raining, so truly only available likely somewhat less than half the year - maybe an extra $0.15 - $0.20 psf/mo added to the $1 psf/mo sounds reasonable.

It may sound nice to pay a 5% management fee but the extra fees can add up to be more than the other company that charges 10% with no add-on fees.