I have heard it’s cooled down quite a bit and assessing if it’s still a worthwhile option to consider as a market for str or even mtr? 

Otherwise every vacant lot would be assessed to have a multistory building on it.

I see them on Facebook marketplace constantly for ~$300 for a well working set.

I understand that that a home in Jerome Village would already have property tax, that would include additional fees for the roads, infrastructure, etc. and that it's based upon "millage" and the home's assessed value. 

I didn't find any challenge finding quality tenants by posting on FB marketplace, roomster, roomies, basically all of the websites. 

Underwriting will assess the performance and appraisal of the property based on traditional long-term rental comps.

I just advertise on Zillow/ Hotpads/ Facebook Marketplace etc. and use a background check website.

This could mean investing in property flips or purchasing out-of-state rentals for more stable income, but it would require letting go of the $1,350 rental income from the manufactured home.What factors should I consider for each option, and how would an experienced investor assess this situation mathematically?

Once you've pinpointed your objectives, it's important to assess your financial situation.

For example, you buy a house for $1,000,000 but you say you bought it for $100,000How do they find out how much you paid for a house to assess their tax?