At the end of the year I had a little spare cash sitting around but I knew that I needed to get at least 3 houses, maybe four roofed this summer. 

I want to flip at least two paint and carpet properties in my spare time and learn as much about the business as I can while doing it.

@Austin Seems strange that an employer can dictate what other licenses and/or business opportunities you do in your spare time.  

It now seems that the perimeter of the building is stable due to the piers, however there was some sort of plumbing leak under the slab in the one downstairs units, which washed out some more soil, and the slab collapsed by as much as a foot, rendering the unit inhabitable.There is a quote on hand for $22k from a foundation repair company to take out the collapsed slab, add some new soil, compact and pour new slab (all of which they supposedly can do without vacating the other 3 units), and another quote for about $130k to redo the inside of the affected unit, and correct other inside and outside cracks around the building and the other units.

So, I'm looking at other uses for the basement to increase cash flow.My ideas so far are (1) building secured storage units and (2) building living space to append to the first floor unit (which would require a compact stair or some such thing).Has anyone found a good use for basement space apart from these or tips on how to do either (1) or (2) effectively?

But hey, if you've got hundreds of thousands of dollars to spare and are looking for someone to pick on, go for it. 

I would then be able to channel the money I would be spending on rent into other properties to flip or rent in my spare time to create that passive income.

If cash flow is your objective and ya have 30 year loans to spare might as well stick with it.

My kids are getting more independent so I get to have more time spare.

The best thing I could tell you is to start listening to the podcast while you're driving or when you have a few spare minutes, those guys are hilarious and full of information!