Just thought I would update this thread now that it is finished.
I went ahead and took the tank down to bare metal and primed it. Once primed I put the decals on using a hair dryer to help smooth wrinkling and masked over. I used an exacto knife and traced the edge of the decals before painting. I was hoping to use a couple layers of paint as well as the clear coat to achieve a smooth surface. Once painted I removed the masking tape and started the clear coat. The decals didn't turn out completely smooth so it wasn't a total success, but all in all I am happy with the end result.
used the flash on this one to try for reflectivity:
same side without flash:
Skull from ebay epoxied to gas cap:
Right side of tank:
These are 2 weeks after paint and I have intentionally and unintentionally got gas on the surface. So far so good, clear coat hasn't faded or dulled.