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. 

The star of Zombie House was buying foreclosures in Florida but there were so many people competing for them that it eventually became a useless source.A couple more negatives: you usually have to pay cash within X hours of winning the bid so there's no financing option.

Eventually he hung up on me as I had to keep asking him to repeat himself because the phone line was just so bad.

Mechanicals will go out, eventually.