.- Many of these HCOL areas also have strict limitations on AirBnB or short-term rentals... that do not apply to owner-occupants - thus allowing for extreme cashflow potential for house-hackers.

Zoho has an in-built dialer and can integrate with SMS services, offering a good balance of functionality and ease of use.Each of these CRMs has its own set of strengths and potential limitations, so I'd recommend taking advantage of any free trials or demos they offer.

If I understand correctly your siblings goals are to sell their rental properties, use the funds to purchase a primary residence they'll eventually move into, and limit their tax liability correct?

It's pretty common practice to have something like that in a property management agreement, and if it falls under that limit they're going to pay it and not notify the owner except in regular monthly updates because it is below the threshold of what is an ordinary expense in the course of business.

I've only had one listing transaction from my BP leads.Most are complete noobs or have limited REI experience with a rental or two.

If you were limited in cash reserves atleast you'll have the HELOC as a 2nd or 3rd back up source of funds to weather storms.

What are the limitations and benefits?

I limited each season to 20 people. 

Simply put, there are a limited amount of PMs that will operate in the area, so I ended up with poor management.

So, you are not at limiting your self when buying a new property.