The property has about 1,500 SF of space that's not being used, so we're adding a business center/study/group project area, as well as a fitness center.

Should I be refinancing to just cover my total project costs to pay back my heloc and other initial costs? 

Instead ask for a couple of projects that he has done, look at the records to see how much they were bought for and how much they were sold for.

Who owns the mineral rights they don't always transfer with the property.Another likely scenario is it could of been a lay down yard or similar for nearby project..

Here are the rough numbers on one of the houses, both are similar:Total investment (acquisition, remodel, carrying costs) - $200,000Current value (after netting out selling costs) - $270,000Potential Rent - $1,500/monthI can do a refi and get my $200K back out of the project, that leaves me with a mortgage payment of $1,400 including taxes and insurance (assuming 30 yrs. at 5.5%). 

I personally have been targeting Dorchester recently because there's a lot of value add projects in that area of Boston.

. $34k), and I've projected that we could pay the remaining $45k by June of 2019 if we keep going at the rate we are now.  

Not to mention the amount of time the place would be vacant while you do the project.

I would like to do more projects with him in the future.

Cool project Aaron!