1. Sounds like you did not wait long enough for the clear to dry. i would wait longer to mask. Testor/MM enamel will get yellow over time, especially disasterous over white paint. Since you are using lacquer, i guess you dont mind using clear nail polish, much harder, dry faster, never peel, but might get brittle sometimes.
2. Krylon is very hot even it said acrylic on the label, I looked at the MSDS and I saw all kinds of nasty stuff in there, so i am not surprise it will disolve your future seal and sip under the tape. I would spray very very thin coat to build up the color. I have no problem with Krylon clear on decals on few occasion.