Future Finish

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.

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.

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.