The builder is in poor health, he's not very mobile and has in home medical care (he can still drive and go to job sites, but is he is very physically limited).

It is often a feeble exercise. 

Unfortunately, cash flow negative investments are not sustainable, so your decision really becomes one of, how much negative cash flow can you support.You have to assume a lot of variables for these types of calculations but in general:[(Purchase price of duplex x % appreciation x years owned) - (closing costs from purchase and sale) - expected cumulative negative cash flow + expected tax benefits + equity from principal paydown] - [theoretical investment with cash on hand now plus monthly reinvestments of negative cash flow above for the same time period you us for years owned - expected taxes from theoretical investment]That exercise will give you the return or cost of your decision to house hack.

If you did physical work to create the lots (ingress, utilities roads etc) then you will want to consider with your accountant whether you have created "inventory" or not. 

I visit all my property every 45 days to change AC filters, bleach out the AC condensate line, test the water heater T&P valves, test smoke alarms, exercise stop valves etc...a quick 10 minute visit which was explained and agreed to on the lease agreement.Sent an email two days ago to schedule it for next Friday at 10am, no reply no acknowledgement. 

If the CA FTB contests your position, you'll need a lot more than that in court as the burden of proof is on you and your advisors, not the CA FTB.A foreign LLC (as it relates to CA) that has a manager physically located in California is indeed doing business in CA as that is both the general definition and the definition adopted by the CA courts of "commercially domiciled in CA".  

If you're looking at working with a specific set of criteria as far as physical property details go, the MLS is going to be the best source. 

I physically delivered a 30 notice to end the lease for two tenants because their apartments need a complete renovation.

I've played with stocks and crypto and still hold both, I also love physical Gold and Silver Bullion (not really an 'investment' in the regular use of the word)Real estate gets me pretty excited and I've been learning about it loosely for the last few months.

I will not lie I have spent several sleepless nights recently analyzing deals in different states to try and get something going it has been taxing physically and emotionally with lack of sleep and nothing really going my way.