Future Finish

Some of us use future only around decal areas, to prevent decal haze, and then coat everything with a flat finish.  No one I know uses it to seal flat paint.

Personally I use Glosscoat to treat the areas where decals will go, then spray almost the whole model with dullcoat.  If I am going to glaze windows/ports with Micro Glaze or similar, I do this after dull coating.  If there are no decals as on very old ships, I do not even seal the paint.  The matt paints last okay unsealed.

I believe I read somewhere that Future and Tamiya don't mix very well. I thin Future with a little rubbing alcohol (makes it spray better) for washes. I then use MM Flat to kill the shine and seal in the washes.

I can't say that I have ever had an issue using Future & Tamiya together (Tamiya Acrylic).

Future should not have a problem getting into all the nooks & crannies - but be aware that when you lay a coat of future down, it may look slightly globular, as if it has to much surface tension, but after a short while it will start to level out & travel into the corners / crevices.

With regards to pressure, I would play around until you find something that satisfies you. I usually up the pressure slightly, but only because a will be using a larger needle. I also find that Future is better sprayed onto the subject from a greater distance than paint as it will not dry up before hitting the subject as easily as acrylic paint.