i just don't see how buying a few on-market properties in a random market gets you very far. 

Again, being said by some with sterling reputations who don't say such things randomly. 

But if you are doing AirBNB just make sure its in a seasoned market that wont have some random policy change that makes it to where you can not use the unit as a short term rental anymore.

What you would want to evaluate is the income generated from the income-producing property(s) to see if the income from your rentals would cover the cost of your new HELOC payment.

However, vacancy means covering 100% of the expenses.Multifamily properties almost always generate higher cash flow due to multiple income streams, which also reduces the risk of vacancies.

It generates a false sense of urgency for the buyer and they are quicker to pull the trigger on the next one without having their questions answered.

This is relevant for multiple reasons 1) appreciation is where the real wealth is generated in RE 2) real estate has tax advantages over cash flow 3) in CA property tax increase is capped.  

If you've been active in this business and actively pursuing a profit during the year, the loss the business generates could help offset other income on your tax return. 

Tel them you sold it and then start asking them random questions that make me seem like I am totally insane

We basically want property to generate some cash flow and long term appreciation.