Just upgraded my speakers - do I still need the subs

If you are staying in the same room and are happy with the KC62 subs, no need to waste money on bigger or "faster" subs. The KC62 and 92 have essentially the same frequency range. The 92's would help pressurize a larger room.

Yes

Yes you will want to keep the subs imo. Unless you have dsp and crossover you would want to set the low pass on the subs as low as possible. 
 

If you have a good crossover time alignment that’s a different story. Cross them over at 60-70hz or so and play with it from there. 

Only you can answer your question.

Yes, keep the subs or get better ones. Subtraction is not going to equal better sound. I ran 4 much larger subs when I had my Ref 1s. Just make sure they are set up well.