Sounds good Michael. Not sure about sealing the decals without actually seeing them 'in the flesh' as it were. I tend to just apply the next decal, then seal. However, there is no harm in sealing first, as long as the sealer is allowed to fully harden before applying the next decal, probably around 24 hours or more, to help prevent any reaction from any decal solution, or even water.
This is one of the reasons why, in this instance, being white, a painted background would cause less complications, and preferably using gloss paint, which, of course, can have the required clear coat (i.e., matt, satin etc) applied later.
To help for future projects involving similar markings, it's sometimes a good idea to plan the painting sequence, as it may help to paint the white areas first (or any similar light tone), then mask this and paint the remainder as required.
This is often easier and more convenient than trying to mask for the white, where awkward angles or protrusions can make things difficult. Once at the decal stage, then the masking can be removed, revealing a clean, blemish-free area for the decals.