My company is licensed in 31 states for owner occupied loans (check my profile) and I can lend in 45 states for business purposes loans (nonQM and dscr loans).

Should we pursue a "cheap" rental in order to build rental history in the hopes of securing DSCR loans down the road? 

Pretty common, you can definitely use commission as down payment conventional loans and not have it count toward IPC as long as you're on the loan. 

Any referrals or recommendations for good and qualified brokers, sellers, property management companies, loan brokers, insurance brokers, mortgage brokers, contractors, etc.

Total profit less closing costs and commissions will be about 42,500 each or 85k total.I would for sure get a construction loan, may be worth approaching 2 or 3 different banks and getting separate construction loans from different banks. 

In San Diego at the current rates for a purchase loan (which has better rates than an ADU additions) at high LTV, I show 1% does not cash flow on a sustained basis.  

Even after one year, that property may provide thousands of dollars worth of appreciation, you will pay down your loan and build some equity, and you can depreciate the asset. 

The seller was willing to take a secondary position on other property assets and provide a 3yr 4% interest on his loan.

You have a decent loan on the place that you won't be able to replace from a cashflow standpoint.So keep at it. 

The Norris Group has a hard money ADU loan, but it's short term (3 years).