The third was a self storage program and because I know nothing about that market I learned a ton from it.

Hey BP! Would love to hear what management software the storage professionals are using to manage their units. A few things important to our team would be a strong screening/application process, tenant and team commun...

I can say that self-managing a STR from afar is beyond me (no experience as a property manager) so that would eat into cash flow. 

I'm looking at fixer uppers that are considered livable (heat, plumbing, etc) and I think my DTI will be sufficient once I get renters on my current quadplex.Just trying to plan ahead, thanks!

I’d conclude that a MTR is a unique market itself, sufficiently different from convention LTR and from STR market to merit it’s own category.  

We also have HELOC's and HELOAN's on investment properties as well, even using bank statements as income, if self employed too.If you'd like to explore your best options, let's talk for a few minutes to determine the best rate and payment strategies.ThanksCraig

I did not do this and was muddling through self taught Quickbooks for years.

Look into a DSCR loan that uses the property's cashflow instead of your personal income to qualify.This is a tax free move as you are using debt plus you still benefit from all the benefits of still owning the first house.Your future self will thank you for stacking houses this way as your cashflow and equity will build up over time creating long-term wealth.To Your Success!

Then you can usually eke out a small profit on the rental income if you self manage and pull your money back out so you can scale with that. 

Depending on your business you also want to keep in mind that some of those funds you take out of that business might need to be used for taxes as self-employment taxes typically don't go away by investing in real estate.