I'm running out of bandwidth to be able to self-manage, especially on the leasing side.

The payoff is worth it in the long run with reliable, on-time rent payments and tenants who are more likely to stay long-term, and take care of your property. 

One of our capital sources are smaller investors and people with money in IRAs that don't have the systems in place, the deal flow, or the underwriting expertise to run a portfolio.

But when I quickly run the numbers it doesn’t add up.

I run a Lakehouse STR and did the same thing. 

If you are looking to be very active and run like Mid or short term rentals yourself, or do flips, then you can, but this does not come without risk. if you are looking to pull money out and put it to work in other real estate so it can appreciate over time so you have a larger base of assets that are paid down or off in the future with some cost now, then I do think that is possible. 10% returns as a passive investor, especially in the first couple years is not likely. 

They’ll run their own calculations and use the appraisal to validate market conditions/assumptions.

How weather proof are they in the long run?

I'm particularly reluctant on analyzing initial rehab costs as I think it would be smart to buy into a cheaper/slightly more run down property as a first.

Because prop was vacant, I assumed its the furnace, as its the only thing that was running.