For good sub integration in real room most probably will be required something like delay, notch filters for room resonances and crossover slopes depending on exact situation (i.e. crossover with flexible settings).and I don't understand your point 1
If you have big problems with amplification of speakers that can't handle LF, high passing it with anything will help.
But high passing it with integrated sub's crossover is not the best available solution IMO.
Standalone DRC processor with Dirac must handle this much better.