If you are looking to build money faster so you can do more upgrades, I would ask if you could rent out the 3 bedrooms all the time instead of just while you are away and then rent the 4th bedroom as well while you are gone.

But, you need to be at least 5% owner for it to count. 

I would not expect that demand to drive up the price in a crazy way but let's say there's some $700,000 4-unit properties in some markets that are sitting for a long time - those will sell faster. 

Another option would be to tell them you have to make decisions based on your investors best interests.Your investing partner could be your significant other, but they don't have to know that.That way if difficult decisions have to be made in the future the frustration would be at "the investor" and not directly at you.

So over 25 years we would be at 1,875,000.

They would probably pay (something anyway) faster and will turn around and bill back to the responsibile party,  in this case the tenant if they agree with what happened.   

At the end of the day it beats renting yourself.

Evaluate the rental market in your area to determine the optimal configuration for maximizing rental income.The choice between using cash flow from your current house to cover expenses or pay off the mortgage faster depends on your long-term financial goals and risk tolerance.

Completely new to this space any advice or recommendation is appreciated.Depends on whether you're in residential (1-4 units) or commercial (5+ units) - typically you want to be at 20-25% down payment. 

@Greg R.It cam be difficult to be at the top of the searches on both AirBNB and VRBO at the same time, because both availability given to the platform and previous bookings on the platform are big factors in the algorithms used to elevate placement.