I would concentrate on marketing the space itself, and allow the tenants to finish it out in a way that suits their needs.

When the lender sends an appraiser out to land that will have a house on it he needs architectural designs, blue prints, itemized costs for materials. 

Bottom line is now realtors dont concentrate on sellers.

I have also been looking in Haddon Twp and Collingswood area....but really concentrating on Oaklyn, that town really intrigues me but haven’t found “the deal” yet.

Moreover, there are long-term savings to be had with a Self-Directed 401(k) over a SDIRA as you do not have to pay a third party fees - SD401(k) plan's cash just sits in a designated account and you, under a trust, control access to it.

Or, will that concentrate the risks so you get weak take-up?

This actually already exists, and agents with the MRP designation like myself get these referrals already.

Plus if there’s a change or design challenge it can really delay a project and cost lots through time.

I go there to get design inspiration. 

., industry concentration):  Look for areas that aren't overly dependent upon a single industry and/or employer.