@Sam Liu you might consider Reverse 1031 Exchange to avoid some of the challenges you mentioned you faced with timing and traditional 1031 exchange. 

Traditionally, I've adhered to the 20% or higher down payment rule to secure better mortgage terms and avoid Private Mortgage Insurance (PMI).

meaning, do you want to be a traditional real estate business representing retail buyers/sellers?

I see this as a chance to do some good and make better money than if I were to go the traditional route. 

There are homes that have a architectural style where they just resemble a traditional log cabin, but are actually wood frame or something else with a foe-wood on the exterior.

The offer complete checkbook control on our (I have 2 partners) ROTH SDIRAs and Traditional SDIRAs.

Please note that we focus on new construction properties mainly, which is different than the traditional "turnkey" model.  

I am not a licensed GC but I have experience building spec homes that I could show a bank Fine paying a higher interest rate on the construction period of the loan, but would like to be more in line with traditional mortgages rates on the perm portion (although fine paying slightly higher if I avoid closing costs for a second loan)Do y’all have any recommendations on specific types of loans for this or specific banks I should talk to?

You buy all the liens with the property if you buy it traditionally.

From your post, I am not sure you need a mentor in the same sense that many syndicators offer mentorship, versus a more traditional mentor.