My biggest concern is with affording the down payment combined with any closing costs or fees that come along the way.I've been speaking to a few different loan officers, and the consensus seems to be that conventional loan programs for a duplex property type require at least 15% down. 

Quick question, it makes sense why I wouldn't be able to utilize the FHA in that scenario but are you sure it would have to be 25 if i went conventional route?

@Sean Thomas a standard conventional Fannie/Freddie primary home loan for a 2-4 unit is 15% down. 

SBA 10% down, conventional 25%.Will go higher than the 12 years, if the market is underserved and we can raise rents, or if there is land to expand.Most people use CAP rates, I'll let them chime in, with their financial targets.Involvement- you will need boots on the ground to service the facility. 

If a builder does it for me he has offered to do it for $85.00 sq ft.....850 sq ft x 4 apts=$289,000.When the 4 plex is finished it will be worth $350-400k....I'm currently being offered a 3.37% APR on a cash out on my home on a fixed rate conventional loan. 

Bank conventional loan How did you add value to the deal?

Conventional Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

25% down conventional.

It will need Cap-Ex sooner or later, so BRRRR would be the ideal approach here; I'm approved for a conventional loan, but could start applying in earnest for a bank loan, or possibly pursue an option I have to partner up to make a cash offer (this deal is right around that 100k mark where my lender would only reluctantly do such a small conventional loan...another reason BRRRR is appealing).

I originally applied for a 30-yr fixed conventional loan for a single-family.