#1
Does double pedal technique improves even if i air drum? you know you open the metronome and pretend you are double pedaling to that but without any drum (to ''destroy'' any missunderstanding i told it like that i don't think anyone is dumb)
#3
Yes you need a pedal there to feel what it's like to be pressing it, while you are air drumming, you have no friction from a pedal, it's a completely different thing air drumming a bass pedal to actually pressing a pedal. The only thing I could think this would improve is timing and speed but unless you have a very light pedal to press it doesn't count for much on a real kit
You are part of the rebel alliance, and a traitor.

#5
Drumming is all about building bridges between the left and right brain, and making the different cortices involved in listening to music, timing, etc., talk to your cerebellum (which controls your feet and hands).

"Air" drumming certainly helps. The only real difference with real pedals is you will now need to build muscle tone to push the pedals. If the neural network is in place, though, that's a simple matter of muscle exercise.

If you want to play metal drums, then study Jazz fundamentals on a three-piece. Learn 3's over 2, 6/8, different "feel" and independent control of each arm, each foot.

There's not a heck of a lot of difference, really, between really solid, funky Jazz drumming and metal drumming except for the execution. Just like Classical guitar will improve your guitar playing drastically, Jazz drumming should kick your metal drumming in the arse a bit!!