Bob, it sounds like you have things in hand.
I wouldn't worry about the 6 pin connector on the psu. There isn't much reference to it's use other than the audio/signalling pins. The pins that have the +12v from the regular battery cable are not connected internally.
Perhaps when the AC psu was developed they thought there was a need to buzz the operator, maybe as part of an intercom system ( or to notify of a brew up).
As to the variac, I use it to avoid the instant on inrush current to the transformer. More important is to keep the ac voltage at 110v max which is a lot lower than most line voltages. It only takes 5-10 seconds to dial the correct voltage. No reason to wait any longer.
Yes, get the tubes tested before applying power. As Chris said if one shorts it can turn a rare psu into a cheap boat anchor.
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