Vacation rentals in these mass-produced STR "neighborhoods" are really just a commodity, similar to a hotel room.

As far as a reasonable fee, I'd say it has to do with the value brought, and product level produced.

BP was bought by a PE company several years ago, and there will naturally be a bit more focus on revenue and profit growth. 

Anything can happen: the market can shift, we can go into another extended lockout period, the property can be destroyed by a natural disaster or by vandalism, the list of contingencies is endless.

If you set them up as a "property manager" who was required to produce X amount of income to you (i.e. your rent amount) and then they'd get the rest. 

Once you pick one give it a serious dedicated effort, but if it's producing no fruit after several months you can always pivot and shift. 

Brett Burky's contributions to Paperstac and the educational content he produces are are unquestionably valuable.

In 10 years it is virtual certainty that a leveraged purchase today would have produced a good return.

That doesn't mean it isn't a good strategy - if the property still produces healthy cash flow after expenses (which includes future capital needs if you've deferred such), at a minimum you could be rolling the cash flow either back into the home to own it outright or using those funds to prepare for your next purchase. 

A marginal producer isn't likely to improve if you increase it's cost of finance.This is where you would sell and 1031.