The existing structure is about 3k sq ft and can be expandable to 6k sq ft (as per the listing).

I’m wondering how to structure my foundation.

You can structure the loan in the 3-4% with local banks if you have strong tax returns/financials/experience/credit.

I would probably verify with local zoning authorities as far as any structural changes needed to the façade of the exterior to allow for a separate entrance but that is likely not an issue in most cases. 

The key issue in structuring a partnership is correctly placing the risk for unforeseen events. 

A lot of things to consider; you need to make sure you have identified a market that suits you, understand its dynamic (net migration, economy, Crime etc...) and then have your criteria fully defined: What type of property, size, what is your business model, what perfs you want, how you are going to structure the deal (JV, Syndication)?

@Zak Marinko as an investor/agent you need the right structure that will allow you to do deals the way you want and make max profits. 

Frankly it makes the deal less valuable to a buyer (as I said no one wants to take on his single user or like an S Corp structure)

If there is an issue for local law, we can coordinate local counsel, but most structuring entity formation is not needed.

A multi-member LLC is taxed like a partnership anyway by default.the business structure is an exhausting discussion.