i've used both dry and wet methods in the past,
wet works better and theres less risk of getting dirt/fingerprints/general shit under the sticker,
i'm no expert like but i will say this,
if you have to put them on dry, make sure your hands and properly clean and definitely put them on BEFORE you build the bike,
if youre really worried about marking them when you build it you could always mask them up,
that way you can get around the frame easier and put you eye down the tubes to make sure theyre aligned ok, you can position the frame, rather than working "around the bike"
i feel for you with the streetbeat sticker like,harshness right there dude, esp if its an original, my hands were shaking putting the challenger decal on the downtube
alot of time and effort can be spent just finding these old kits,
best of luck with the next one