What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

@Deborah Wodell Please see  zillow history and Redfin history for that area and see if it improved in value over 10 years and then conclude whether it is worth to keep it as a rental or sell..Usually to become wealthy one should not sell Here is a great book for youhttps://www.coachcarson.com/building-wealth-one-house-time-j...

There are areas that restrict rentals to 6 months out of the year.

The tax advantages of buying/holding gas stations are pretty great.Many of the components of gas stations including pumps, tanks, external parking areas, and other equipment are classified as either 5 or 15 year property so you can bonus depreciate a lot of it (minus the land value) and get significant deductions in year 1.With the current bonus depreciation rate at 60%, a $1 million gas station acquisition could still lead to $100K+ in year 1 deductions depending on the specifics of your deal.

If you had 50k in credit card debt for business startup costs (not real estate) with a 3-4-year plan to pay it off, high debt utilization in the meantime and a 620 credit score - but wanted to start investing in rental properties - what would you do with 20k that falls into your lap?

If the house you are going to sold was your owner occupied primary residence AND you have occupied at least 2 out of the last 5 years all gains up to 500k a exempt from taxes. and remember equity and gains are not the same thing.

The second year, they all of a sudden at renewal sent a notice that I'd be required to have carbon monoxide detectors in each bedroom. 

The property is 100 years old but has updated wiring, plumbing, and units.  

Housing Market ConditionsMedian Sale Price: $395k• YoY Price Growth: 8.7%• 5-Year Price Growth: 50%Housing Inventory: Less than 7,000- low (Below pre-pandemic levels)Property Tax Rate: 0.42Average Insurance: $1,680Median Rent: $1,895 (single-family house)• YoY Rent Growth: 1%• 5-Year Rent Growth: ???

There are lenders who will let you pull out 75%-80% or so, possibly based on rents vs your own income if you don’t qualify that way, but their rates and fees will typically be higher than conventional loan products, and you may need rental history to go that route.