If in doubt about the quality or state of the decals, give them a coat of clear, sprayed on, but leave them at least 6 hours before using them.
The gloss coat applied after the decals is used to give the model an even appearance, with the final clear coat to give the desired finish - gloss, semi-matt or matt, for example.
The clear coats seal the decals against fading and cracking. The Micro Sol/Set is what 'pulls down' the decals onto the surface, eliminating silvering and making the carrier film virtually disappear, making them look a if they're painted on.
The decals need to be applied to a gloss surface to allow the Sol/Set to do its job properly, and using the sequence described, you should end up with a perfect result.