My suggestions would be in this order:(a) Determine the type of financing you qualify for - this will short cut the process considerably and save time on investment angles and next steps.

@Julie Doke: Industry specific software speaks to you and you can easily relate it to your day to day process.

Any success with a subto deal for your primary residence? 

The process was fairly smooth for me.

If he’s open to it, that could reduce the upfront capital you’d need while making the process a lot smoother.

The lender will require that you live in it for 12 months and then you can rent out all of the units after that and start the buying process using the same strategy all over again after that 12 month period.  

If you need to obtain it, how difficult will that process be?  

Quote from @Sami Gren: I start by making the original tenant fill out a form requesting to add a new renter, and they pay me a $50 processing fee (I charge a $50 fee any time I make changes to an existing lease). 

I'm trying to analyze my first property and not sure how to set it up to run the number using the calculator tools here. 2 of the units are successful Airbnb short term rentals, and the other two units are month to month rentals to existing tenants.

It seems like they help you find a deal, work through the process, sometimes property management etc...