This would give me the ability to solidify the foundation permanently for the entire property.

Once you move out and it's an investment property many of the guidelines lenders use will change so just a heads up to put in place solidly, fairly permanent financing of this one before you make the change.Congratulations on your thought process, you are on a solid path for success!

I have 3 properties and I use them year round as event and vacation rentals, never permanent tenants.  

My only advice is that if she is your girlfriend not yet your permanent life partner as a wife or fiancé your best bet is to stick to your gut just in case tomorrow she decides or you decide that this relationship is not valuable anymore and to part ways.

It cannot be your permanent residence.  

It is amazing how many homes have permanent sandbags all around them.

I have been called back because of leaks in exposed fasteners, but it was not a permanent problem.  

Our plan was to buy with little down,  live in one unit and start construction on of a permanent residence.  

Unlike manufactured homes that do not appreciate, the modular homes are technically appraised as a regular site built home since there is no trailer, it’s built up to code and has a permanent foundation.

@Michael Frank I found a construction to permanent loan so there was only one closing cost.