CMU is a very durable material and would actually be stronger than many during an earthquake... not sure that should deter you.   

Is the expectation he will work for “free” (only pay materials) and then split the profits after sale?

I am looking actively for deals and I always struggle on figuring out how much a property will rent for.I am finding lots of potentially great deals, but a hundred bucks in rental income can really affect the ROI.Which materials to learn?

Durable, pretty cheap on materials and labor. 

I made a judgment call and charged him 50% of the material costs, none of the labor.I believe it will cost you at least $200 to replace the stove top.

Ordered all the materials on-line so just waiting for the delivery.

He said for the extent that his camera could go he could see there was a lot of cast iron debri He suggested that I shouldn’t proceed unless the seller of the property can create access to the stack line (clean out in the bathroom wall) or install a clean out outside for external access rather than having to rip out the toilet each time there’s an issue.

The woodstove is installed correctly, with correct clearences to combustible materials (including the chimney setup)2.)

Whenever he needs money for the first draw or for "pre-ordering materials to be used for the second phase" he's Johnny on the spot with communication and texts/emails/calls even after his supposed "I don't answer calls or texts after 5:30 so I can keep my wife happy" rule.  

"To qualify as a real estate professional, a taxpayer must meet the following two criteria (IRC Sec. 469(c)(7)(B):More than one-half of the personal services performed in all trades or businesses by the taxpayer during such taxable year are performed in real property trades or businesses in which the taxpayer materially participates, andSuch taxpayer performs more than 750 hours of services during the taxable year in real property trades or businesses in which the taxpayer materially participates."