I thought about removing the front driveshaft on this truck I'm just worried about the output shaft of the tranny. Would I need to plug it with something or what?
The front driveshaft is connected to the transfer case, not the transmission. And it bolts on, it isn't a slip yoke like the rear driveshaft into the transfer case. So it's not a problem to drive the truck without it installed. I drove my truck without the front driveshaft installed for about a week when I was getting it lengthened.
OP, as stated above if you aren't going to do them at the same time I'd highly recommend removing your front driveshaft. If you did accidentally put it into 4wd with the different gears front/back you will destroy the transfer case.
Cost wise you're probably looking at +/- $3000 to do the swap. You'll need a front diff from a 2010 or 2011 in order to change the gears as the ring gear is welded to the carrier in the 2012+ trucks. I believe the housings in the 1500's also require a bit of machining to fit 4.56's in them.
For gears I'd look at AAM (OEM) or Yukon.