Your not correct under many different circumstances.First property tax is 1.1% (fairly safe) with 2% annual increase (prop 13).Next expenses include a lot more than property tax and interest. 

I talked to Padsplit and they manage SFHs renting each room to different tenants - the total rent is more than renting it out to one household.

How long it takes to be financially ready is different for everyone.

Same basic structure they asking price is a suggestion, I offer what I think is a workable number for me and we negotiate to the "middle";  though the middle is not halfway, we never "split the difference". 

Look at buying my first investment property (probably a house in the 100-150k range) and begin looking for a tennant.I can imagine there a lot of different theories/ideas with what one could do here--I am just curious to see what other people think.

Every state has different laws regarding a notice to terminate/non renewal of lease.

I'm telling you this so you don't get confused when talking to different lawyers. 

But it really makes a difference.

Since you're looking to expand into Florida and other states, I'd recommend starting by narrowing down your focus:Market Research – Florida has great opportunities, but each state and city has different laws, taxes, and demand drivers.

Where can I find the info on how you group the different neighborhoods into classes?