And are you dead set on having raw or scraped land to build your own home, or are you possibly looking at renovations/updates to an existing structure?

@April S. a tenant and a seller are not the same thing and the process for retaining possession rights to the property are different depending on which it is you are actually dealing with. 

We were hoping to salvage existing tubs, but once we cleaned them up we realized that the grime was hiding some cracks and chips in the fiberglass.

Probably based on the owner's existing relationships. 

One end of each bedroom was stripped to the studs for the installation of 3x8 closets that didn't previously exist.

They may need to wait a year or two and show proof the payments are getting made.Realize this does violate the due on sale on the existing loan.  

@Mark Sossoman, most attorneys won't even touch any type of deal without a retainer of some sort usually between 5 & 10k if they're worth their salt.

A dollar amount and the phrase "for good and valuable consideration" may or may sufficient in a transfer of title and may not be the same as described or required in a purchase contract that conveys an equitable interest.Mixing these two concepts is incorrect.When a purchase contract is made, legal title remains with the seller, but equitable title is given to a buyer, full title is in  state of limbo until settlement.Equitable title must be financially measurable, if it is not measurable or cannot be established and is an amount customarily accepted, equitable title may be limited or may not exist.

The credit line has about ten months before interest is charged and thus allows time for investors to pay into an already existing investment.Should I meet with a lawyer and draw up terms of agreement for them to sign?

I'd suggest you look to TREC as to your wholesaling activities and read the forums.Talk to your lender, if you have experience and are otherwise qualified, you can use a blanket loan on your existing properties and the ones you acquire.