Do I add the $15K to $30K-$40K rehab as an all in at $55K and pay the existing mortgage on the home?

Many seniors live on a fixed income, so you can't just push their existing rents as their benefits probably aren't keeping pace. 

Existing Tenant fills out "Add A Tenant Addendum" that spells out the process and requirements.2.

That is much cheaper than the minimum of $2,000 I have to pay just to swap out an existing gas furnace, assuming there are no alterations required for the duct-work and vent systems.$1,000 buys a LOT of insulation. 

If you find you're unable to get something right away due to your credit or income situation, you may still be able to acquire your first place creatively via a lease/option, seller financing or buying a place 'subject-to' the existing financing, plus there's always hard or private money however either of the last two would require having 'take-out' financing lined up in advance, which might be a stumbling block.

An existing Facility that's being properly managed should have an expense ratio of 32 - 35%, that is the industry standard. 

“Austin is growing rapidly, and as we look ahead to accommodate existing and future Austinites, there needs to be a plan in place for a more affordable and sustainable city,” said Dewitt Peart, president and CEO of the Downtown Austin Alliance.

You actually want / should to do this with vague information (i.e. no live deal) so that when the time comes for a live deal you've built the required pre-existing relationship.

I know it's not ideal to just lay shingles over the existing roof, but is it worth asking the seller to address more than just the leaks? 

I just docusigned title documents except for one box: To our Knowledge there are no existing violations of county ordinance etc..... -  What happens if I check this box??