first make sure that the motor's gonna fit with that funky frame. (you probably already have, i'm just saying...) and make sure there's no cracks, or other problem areas.
the best prices i found on all the parts you need are at bikepartsusa.com.
they've got the best prices on shipping, too.
rear wheel, $40.46: Wheel Master 26x2.125, Rear, B/O, C/B, H/D, Chrome Steel Wheel | BikepartsUSA
(chrome kinda sucks, but the shimano coaster brake is great.)
seat, $16.38: Pyramid Cruiser Saddle With Springs Black | BikepartsUSA
(these are awesome. high quality, cheap, and super comfy.)
(and no, i don't work for them, i just buy a lot of stuff from them.)
the rest of the stuff you can look up for yourself. dunno about the springer fork. i mean, i like 'em, they just don't seem to work with the added weight and the pounding the bike takes. most people end up tightening the spring down so much it ends up being just for looks.
but whatevs, my opinion is, if the motor fits in that frame, do it. better to have something different, than to follow the crowd. and despite the age of that frame, it's still (probably) better than a walmart huffy.
also, money permitting, you can find the original rear rack, tank, chaingaurd, etc. for that bike on ebay or craigs. they're always popping up.