There's always going to be some cost to metrics, going forward you probably just want to document it and then update the figure as you tune it. Higher performance opt-in metrics are the sort of thing a company using it at scale ought to be able to help with/sponsor work on.
Absolutely. The plan is to make it opt-in for now, and then having a company sponsor the performance tuning would be very welcomed. Otherwise it'll probably sit until someone with the right skills/know-how and time comes along.
