They claim to market on dozens of online channels, and they seem to know the right amenities to feature, have great design, services, experiences etc.

In order to get there it would be good if you could keep feeding cashflow proceeds back into acquisitions, on top of your continued W2.Speaking from experience, you can manage probably 30-50 units yourself nights and weekends before you really need to hire someone.

I would try to find an agent with investor experience and, ideally, a focus on investment properties. 

Does anyone have any experience of getting into real estate this way?

I have no experience there. 

With 30 years of experience in real estate and now owning a quadplex, duplex, and a condo STR, you’ve already built an impressive portfolio.

@Monty Alston It has some impact but no lenders will give you credit for having experience building a home unless you have built or renovated a home in the last 3-5 years.

Quote from @Drew Mullin: I have some experience in the south Florida area.

I pay attention to local amenities like shops, parks, and restaurants, because they make the area more appealing to tenants.

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.