Even with my income, most of my money goes to taxes.

Why spend thousands of dollars in points to get the rate down to 6.1%, if the normal interest rate is 6.1% in a year and you can buy it down to 5% or 4%, etc.Nobody knows how low rates will go, but with the fed signaling that they will likely begin rate cuts in Sept, it's certainly a good sign. 

Tell the buyer to come up with more money down 

I was on a job with a gas crew and asked the same question and was told that all of the work that they would do would be of no charge because they would make more money once the units were separated.

Fannie Mae or Freddie Mac won't touch them.Many buildings allow STR because they realize there are a lot of out-of-state and foreign national buyers wanting to place their money in the Miami real estate market because it is such a good investment.

And ideally sell it 4 years later.If I can more or less count on the renting of additional bedrooms to cover the running costs of the house, I'm really only looking at taking a hit on the buying/selling costs - which SHOULD be lower than what it would cost to house him in dorms for 4 years.I feel like this is pretty obvious and easy (not trying to make significant money here, just thinking I could save $10-$20k on housing costs over 4 years).

I had finally landed a great job making great money but still barely getting by.

When my handyman came to the property, I would give him the list and a credit card, and he would spend the afternoon driving back and forth to Home Depot.

Likewise, your payment will be slightly lower and you can continue to cashflow more and still get some extra money to reinvest.   

Roll it into the rent with a lease clause that anything over $X is split 50/50 between both tenants and you don't care who uses more water...In short, spend some money and make it a legal duplex or at least make it two separate units.