It has been difficult to find a mud jacking firm that will fix my leaning stoop, so am starting to consider demo and re-pour.

As a property manager I helped a new client with a portfolio he bought on default from a lender unfortunately 3 of properties were scheduled for demo already when he closed. 

How big of a house can I build on this lot if I demo the current home and build a new foundation?

My question is more centered around the demo/framing portions of the projects.

I spend hours house hunting, going to open houses, looking at comps, and demos just for fun -- so I think naturally becoming a Realtor would be in the best interest for me?

No way you'll be able to build a house for that cost (including demo) and hit the price point you need to.

If not, the repair should still be under $1,000 if you can find a cheap handy guy to demo that and redo it.

Requires some training in the beginning but you can take a demo/framing guy and train him to be a finish guy also. 

For a 2/1, I received these quotes with permits 14k electric,  8k furnace/duct, 2k central air, 2.5k floors sanding/ synteko, 10k bath,  12k kitchen, $30/$50 sheet of drywall,  3k paint,  roof was about 7k, demo 3k, concrete demo/new $12 s/f, windows $250/$400 depends on brand, then GC fees,  etc. 

So if he decides he wants it back he can buy me out and I still get my $$.What gave me the idea was our city auditorium was slated for demo.