Do those properties fit with your strategy. 

This can cause their plan to pause or not work out as they hoped.So, when you're shopping around for mortgages that fit your situation, be careful.

Save for Your First InvestmentCommon Pitfalls to Avoid:Don't rush into deals without proper due diligence.Avoid over-leveraging or taking on too much debt.Be cautious of "get rich quick" schemes; successful real estate investing takes time.Don't neglect legal and regulatory considerations.Remember, everyone's journey is unique, and there's no one-size-fits-all approach.

Google 501c3 and see how your idea fits within the IRS regs. 

Given my situation (see below), what real estate strategies are the best fit, what are the typical ranges of returns on them, and what are their other pros / cons?

You will know from your conversations who is a right fit for you and who is not. 

I am thinking that house hacking is the best fit for me, since I am currently renting with my girlfriend.

If you cannot make and accurate assessment of what will fit on the property than you cannot make a proper evaluation of value.

Maybe she just wasn't the right fit but it makes sense to me why a lot of long term tenants might not like the arrangement. 

If I were in your shoes, I would first evaluate the area, and if it fits my criteria and I know what kind of tenant I can put in there I would continue to the next step:Finding out how much it would cost to rehab and what kind of rents I can achieve.