The rest I invest , the plan is to eventually take a nice Tax free distribution to reimburse for past medical expenses.

My goal is to start buying rentals, and eventually transition out of the medical field over the next ten years, (or less if possible).

It doesn't put money in your pocket, and it will eventually depreciate and outlive its useful life.

I'd love to start buying up investment properties, with a goal of two a year for the next few years.My main concern is this: if I finance these investment properties with conventional mortgages, could I eventually disqualify myself for a mortgage on my primary residence due to increasing debt to income ratio?

You may eventually want or need to sell.

I plan to flip houses down the road eventually on the side, so I thought this would be a good first experience.

Hopefully this will get better as time goes on... or eventually becomes unnecessary.  

Still humming along on my mostly LTR conversion. but concerned about if they can no longer pay eventually.

For the most part these people will eventually revert back to previous financial habits and you will want that extra month of security to protect yourself for when things go off the rails. 

I'd recommend setting up a new LLC for each project to start out with the idea that you're building a brand and will eventually build your own fund.