For longer-term investments, what is the best loan option: conventional? 

Will a conventional lender use the 3k or the 1.2k to factor my DTI?  

Next, We are looking to put about 160,000 down, Would it be smart to finance the building and the assets with one conventional loan?

There isn't a ton of inventory where I am.

Hello,The inventory of investment grade SFRs has completely dried up in my target markets on MLS (foreclosures and short sales).

From what I have read, with conventional loans, yes.  

There are other ways of getting loans besides the conventional ways.

if so they usually require you to live there for a year i believe. if its a conventional mortgage, you have nothing to worry about, that shouldn't trigger a due on sale clause, because your not selling it, you are still owning it. disclaimer- i am not a lawyer.

You mentioned 80% LTV, but unless your are not using conventional residential mortgages, that will not be possible for multifamily.  

And will expect you to refinance out to conventional lending within short order.