Yes and yes. Coat with Future and let it dry or cure overnight before applying decals. The future produces a smooth surface for the decals. After puting on the decals, you can then coat with a dull coat. to get the flat texture you need. It will also help seal the decals. I always apply a second coat of future over the model after I have put on the decals. I will then spray a dull coat over it and this gives the decals that painted on look.
Berny
Phormer Phantom Phixer 
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.