The property can be turned into a four bedroom 2 bath (through space in the basement) which would increase the rent potential substantially. 

Rents hadn't been increased in years.

I am talking about placing a factory built home on a permanent foundation with that home built to the same national standards as used for traditional stick built homes. 

The procedure is they have the contractor fill out 2 forms, they send an inspector to make sure the work is done (to some standard, I would guess), approve it, send me the money, and I send it to my contractor.

I'm the type of person who likes to standardize everything.

If you buy a home from a homeowner who is living in the home, is there a standard amount of time for them to be allowed to live there before vacating, while they look for another place to live and move there?

https://www.har.com/content/newsroom/Houston Real Estate Highlights in October Single-family home sales increased 4.7 percent year-over-year, with 6,716 units sold;Days on Market (DOM) for single-family homes was 57 versus 61 a year earlier;Total property sales rose 6.0 percent, with 8,127 units sold;Total dollar volume jumped 9.3 percent to $2.3 billion;The single-family home median price climbed 3.6 percent to $234,653, an October high;The single-family home average price also achieved an October record, rising 3.5 percent to $294,500;Single-family homes months of inventory reached a 3.9-months supply, up fractionally from 3.7 months last October, but below the national supply of 4.4 months reported by NAR;Townhome/condominium sales dropped 2.9 percent, with the average price up 4.9 percent to $206,838 and the median price down 2.2 percent at $152,900;Leases of single-family homes rose 7.3 percent with the average rent down 1.1 percent to $1,754;Volume of townhome/condominium leases fell 6.8 percent with the average rent up 1.2 percent to $1,550.

As your assets increase you may want to get a personal umbrella policy (PUP) to cover any additional liability.

We are looking to perhaps move into a larger place, and rent out our original duplex, which would increase our monthly cash flow even more.

Any local banks in Texas I've talked to have quoted 20 year am, and when pressed, state that that's 'standard for commercial' so yes, your 30 year am is great, and probably makes it more worth it for that higher int rate.