No. None of the kits will fit.
I believe it is a5/x7 threaded.
Yes, and in fact there is an E-trigger addition that comes with a double trigger.
No. The trigger assembly for the a5 is set up very different from the 98 custom.
An E-trigger is the Tippmann Board, not an actual trigger.
a new trigger
No.
No, the E-Trigger only fits the Tippmann they're designed for.
The Gryphon has nicer features, like an asa on the grip. However if you plan on playing for more than a few months, you should buy a marker at least in the 100 dollar range if you want it to last.
No.
No, it will not fit.
Yes, just simply buy a double trigger and double trigger guard, open up your marker, remove and replace the old trigger and trigger guard.