Powerlet heated gloves need heated grips to assist them for me. In the 30's my hands still get cold even at max power. There is also a hot spot on my left pinky that will get a burn while the rest of my hand is cold. Left one quit working this weekend.
As for the power I would get the high power jacket liner and not a vest.
You can always turn down power consumption but it's there if you need it.
On the ST1300 you should have enough power for 2 sets.
Took a ride to SO's daugher school this weekend. 4hr round trip.
SO had my heated jacket cranked, gloves (make that glove) cranked and glommed the liners out of my pants to put over her leather pants for the trip back. Yah know cause it was SO FREEZING (50?)