Biggest drawback is the time, they are slow.

In an attempt to clean up the industry, legislation was written by those who 1) had never been lenders themselves and had no understanding of the industry and 2) their biggest campaign contributors were big banks (look up Barney Frank, Chris Dodd, and Elizabeth Warren's campaign contributors at the time and you'll see big banks).

I know the general basics of the market, the business model, etc, but I was hoping to take my knowledge to the next level.My biggest goal right now is to own a rental property before I graduate college (currently a junior in high school).For context, I love reading books about investing and personal finance (I have a very solid foundation of knowledge built up) and I currently have a portfolio of about 11k between stocks and crypto. 

What is the downside to this? 

What are the biggest challenges people face when underwriting a deal? 

I invest using BRRRR and what I've seen lately as the biggest obstacle to that strategy, has been the initial hard money lenders, with the recent market changes this past year are doing lower ARV percentages ...example going from 80% ARV down to 65-70% ARV to mediate their risk, requiring more out of pocket initial money's. 

The biggest issue we are running into at the moment is finding a profitable multi-family unit and how to fund it.

Some people treat their STR like a hobby and others treat it like a business.You don’t know the numbers are based on if owners use it 3 months a year themselves, or manage it themselves and have STR knowledge or farm it out to a competent or incompetent property manager.In one area I invest in, the biggest players are all large direct booking sites with hundreds of properties so their revenue doesn’t show up on airDNA, etc.Use conservative numbers and understand your skills in terms of getting a property to be unique, marketing, listing management, etc. or the competency of the PMs you are interviewing.Good luck!

Are there any foreseeable downsides to this conversion?

They get no upside but are downside protected because if you did not pay him he could foreclose on the property to collect what is owed.