Questions about using JBL LSR4328 mains w/ Event 250S sub

[promesis]

I replaced my old Event 20/20P's with a pair of JBL's LSR4328.
I had been using the Event 250S subwoofer with the 20/20's - positioned on the floor directly below the R Main .. ( i am in a new room and do not have a sufficient reference to judge the sound of the Event System, as a whole, verses that consisting of the newly added Mains)

The Manual for the 250S sub-woofer states proper settings for XOver Freq, Polarity Invert, Phase Delay when using specific Event Monitors depending upon the Sub's position in the room (circle). Additionally, that when coupled with non-Event mains that the "starting points" for Polarity Invert and Phase Delay should be set to "off" and "0º" respectively.

The newly added LSR4328's have a published frequency response at 50 Hz to 20 kHz.

Goofy newb questions:
What should the XOver Freq be set to .. 49-50 Hz?
Is the general crossover concept in this configuration to leave a small gap between the lowest freq range of the mains and the sub's crossover setting?
Should I engage/disengage Polarity Invert and pick the option that produces a more pleasant* or present* bass character?
Should the Phase Delay be adjusted in any particular way?

Thanks for any time and attention to this.