The new listings I have seen are laughably expensive (mortgage is 2x rents for example). 

The area here is pretty desirable and typically houses have appreciated around 5%.

This is a great example of why REALTOR contract forms often suck.

For instance they will need to disclose their fees up front as an example.

I typically only work with people I already know but I do get a lot of calls on my listings from strangers about various things (unrepresented buyers wanting to make an offer, sellers looking to list a similar property, all sorts of scammers and salespeople, etc.). 

That's a typical scenario and could cost you $10,000 - $15,000 so that would be a good starting point for your reserve.But there's more!

For example I used my current house hack to pull a HELOC and bought out of state.

Typically brokers represent the borrower, so this is something you want to find out ahead of time.

For example, lets say you close on May 7th.

Everything she has written appears to be opinion and not factAttorney will deal with this and tell her “I have forwarded everything to our attorney and please forward all future communication to them”That typically gets them to pull back quicklyYes it costs money - that’s reality of being a landlord