Of course it's personable and will depend on an individual's financial situation and "how much I want to deal with b.s. factor"  I was looking for some general rule of thumb like "never take less than 80% of fair market value" like 20% down is a general rule of thumb for purchasing a property through conventional loans.

Biggest factor is determining market value for each house and the market rents. 

I will look into my AGI and see where I land in that category, as for what I see right now that will be the determining factor. I

For example, if a major corporation is opening a factory within the next year, that will create 1,000 jobs over a 3 year period, is that a good incentive to potentially invest in that city?

If it is just an area with expected higher cash flow due to nature of tenants and lower quality area then no I won't touch it.The other factor is how much time this might take away for that expected 6,000 gross cash flow versus your other business practices.  

There is some specific wording I'm seeing as follows: "on the unpaid principal at the rate of 5.4% per annum; principal and interest payable in installments of $2643.04 or more on the SAME day of each calendar month" Trying to read through the rest of the note is confusing, and I'm not quite sure I'm understanding it in its fulness but another factor is if the buyer defaults and can't make any more payments, my in-laws will reclaim the business (this is in the note).

The benefits of off-site fabrication are plenty: There's no inclement weather to worry about, there's more efficient sourcing and utilization of materials, less material waste in the factory, less site disturbance, less neighborhood disturbance, less soil compaction, less erosion from construction activity, better quality control, larger purchasing power, there are many more.The modular fabrication market in the United States is disturbingly inadequate compared to what's happening across Europe and Asia with the adoption of robotics and automation in their production.

Too many buyers and possibly even too many inexperienced buyers.Also, not to ignore the supply side, despite a lot of construction, there is still a shortage of new construction in many areas.One final contributing factor I would site is the increasing use of multiple years of IO (Interest Only).

I was there this week for a visit to the Volvo factory (I'm a dealer in NH) and while there heard some incredible stats on SC/Charleston.

Another factor is the incredible wealth building by appreciation when borrowing.