No advice as I think my savings account earns maybe 1%, so I'd also love to hear from others.

This platform on Bigger Pockets is a great source of information where you can ask questions and also learn from other investor questions.

"Subject" to other factors that is where you wantto either buy or build first.

We own 3 other rental properties that have a 6.5%-7.5% APR, and no credit card debt or any other high interest debt to pay off.

My primary is a 2-family also and I use turbo tax for that and my other rentals. 

Or is it other factors? 

One simple example, if you take two rooms and rent another 4 rooms, you will have two cars and each of the other tenants will have at least 4 other cars making you house to accomodate 6 cars.

Consider that an advantage you have over most others.  

I have an instance where two tenants, a mother and a teenage daughter are using 3X the water of the other set of tenants, which are two sisters.

This was 2015 so although it didn't cash flow, the other unit offset my mortgage by quite a bit.