ROI = (PMI saved/extra downpayment).

Assuming the mortgage servicer eventually gets the misplaced principal payment, you will have overpaid the principal of the mortgage when you make the supplemental monthly payments, and the mortgage servicer should return that extra principal to you, without question, when they ultimately close the books.The mortgage servicer will not return the interest portion of your payments, and in fact some additional interest may be due when this is settled, despite your ongoing payments, because the interest is collected in arrears.  

ARV estimated to be between $725-875k.So I'm wondering if the conversion from duplex to fourplex is worth the extra renovation costs.

HML's will want a first lien position, so if you have financing in place already you need to look at a refi that gives you the extra capital you need to pay for the rehab while replacing the original loan. 

@Sam Horton Thank you for the feedback, I am planning on using my VA loan, I am blessed to receive extra benefits from the armed forces, will I need an LLC or do continue without, should I acquire a real state license or not?

The reality is the opposite - if it's not in writing then the PMC doesn't have to provide the service or can charge extra for it!

Then if you go the extra step and Airbnb your space while you are gone, you would definitely be able to live for free (and comfortably) and possibly pull in some cashflow. 

I am looking to buy my first investment property in US but the problem is that I am currently living in British Columbia, and I am only an immigrant here.

The reality is the opposite - if it's not in writing then the PMC doesn't have to provide the service or can charge extra for it!

I always hire my own inspector, and get a walkthrough video of the house from them (something not many people bother to ask for but it's really easy for them to do and doesn't cost any extra).