Audio Research REF3 tube question clarification

Audio Research REF3 kindly clarify.

Do the 5 Sovtek 6H30PI tubes have to be all matched to get the best sonic performance?

What do the 5 tubes actually control?

Hours on tubes, when should they be changed to get the BEST sonic performance as there seems to be different opinions.

Sovtek 5 tubes, some say change them up to 1600-1800 hours but other sugest 3000 hours, which is it?

Winged "C" (SED) 6550C tube, some say change up to 800 hours but others sugest 3000 hours, which is it?