So bump the 5-7% on maintenance to a good 15% (sometimes more), and try to exchange things that rust easily with something that can last more in "near the coast" weather. 

I made 15k on this deal, but it easily could have been 25k if I negotiated better at the beginning (and my inspector wasn't terrible) and I also listed it too low. 

There are more advantages to multifamily that you can easily research online.   

I can easily google for 50-200 acre plots of undeveloped land all over the U.S. for under $100k, but I'm thinking there's another level of scale I'm not seeing, such as government grants, auctions, etc.

And why would two professionals making that kind of money want to lock into a three-year rental when they could easily make enough to buy a home?

The lot is easily capable of holding 2 residences.

I think the hard money loan would be the best route to take as I am confident the upgrades could easily bring the value up to around 150k.

The reason for this post is because, if I'm buying a property, and I can easily afford to mortgage, why is the PITI requirement even a thing? 

I would encourage you to do more research before jumping into this or be mentored by an expert because if you don't know what you're doing, you could easily lose your shirt. 

Luckily real estate is pretty cheap where I live.Taking out a mortgage for real estate is foolish unless you are fairly wealthy and can easily weather it not being rented out/rented out for cheaper than it really should be.