In my former life(pre real estate).  

If you have the time and money, I would highly recommend taking a RE pre-licensing course since they are so easy in NH.

I was pre approved for a loan with a 10% down payment with the understanding that it would be owner occupied (there was no discussion of single vs multifamily in the pre approval process) and I'm under the impression that I may even be able to qualify for an FHA loan which would allow for an even lower down payment?

-Pre-Arrange any early withdrawls with your attorney and see Gold Rule above.

(We're both 24)We just got pre approved for a loan a few days ago and I have started reaching out to realtors to hopefully find one that knows multi-family properties as well as the Haverhill area.  

You can have a custodian for a self-directed IRA (SDIRA) roll your traditional IRA right over and you will avoid any tax implications.

i am looking at a commercial building asking price 1.5million, 15 units 13 are occupied.rent roll is 171k when fully occupied, presently its 131k expense are 60kthe seller is not motivated, so how do I structure the deal so we both win. 

Agreed with @Ali Booneriding the stock market roll coaster is never fun however its good you are seeking other alternatives 

I would like to turn it into a 3 bedroom single family.How can I pre-determine the value after rehab?

With that being said, I'm working on a basic plan of action so I can get rolling.