I think #1 is most realistic but I do want to duplex it in the near future.

The expected balance at that time is estimated to be around $2,100,000.00 based on the same website. 

Hard to say where rates will go for sure, but we don't expect them to be at this level for longer.  

What kind of rates can I expect?

Food for thought - you'll also want to consider your tax strategy and reported income through the lens of your future plans.

I would expect the cost to be about $800 to $1,200.On the other hand, perhaps you would consider gifting it to your son incrementally.

In the future ALWAYS send notice VIA writing (whether VIA text or registered letter) and not verbally. 

People can deal with a 5% increase (in this case 100-150), but a 10-20% increase is more likely to bump them out.Also remember that you have to hedge against future markets in which you will not be able to increase rents. 

The median house price is north of $400k, what do you expect for houses 50-75% of it?

If the lenders are ok with it it could be a great cash flow strategy.One more thing to consider is what a future potential buyer might think of the strategy.