And really loved taking advantage of the pre 2008 rules.  

Two of the tenants seem to be ideal with rent being paid on-time, considering it being put in the mail, etc. 

I have paid on them for a year.

As your loan gets paid on time, and you show a positive trendline of increased DSCR I'm sure you can ask to remove this quartlerly requirement.

You will need to combine the knowledge you learn here with your knowledge of your local market, and likely that of a mortgage broker and real estate agent in order to determine your best plan of action.You can call a mortgage broker and find out how much you may get pre-approved for.

I effectively paid little for the illegal units when I brought the buildings (say $200 PSF), but the square footage is good, they have respectable enterances, decent light, amenities, etc. so it’s worth the hassle of dealing with the city.

Even the paid software systems will usually give you a couple weeks to try out their software for free.I recommend looking around and narrowing it to 3-4 different systems.

Simple for putting the seller and buyer together you get paid a fee .

Before I even start looking at properties should see if I pre qualify on a loan correct?

You would have a lien against the property so you get paid off when it's sold.