When I tighten the brakes onto the cable I make them tight enough that the cable gets crushed becuase i dont want the cable to slip out. Then afterwards all brake adjustments are harder because the cable is all deformed... To i have to tighten it that hard?

You have to tighten it hard enuf to no slip - so, yes, a little crushing is inevitable.

It should have no bearing on brake adjustment.

tighten it, grab a fist full. if it slips, tighten it a bit harder.

what you don't want to do is over tighten it and cut the cable strands.

Yes, you do have to crush the cable to achieve a secure hold. It's the distortion (crush) that ensures that it doesn't slip when apply the brakes. Also note that the cable is most likely to slip when under the greatest tension, such as when applying emergency braking force to avoid a collision, obviously when you least want a failure of any kind.

Normally brake cables are clamped only once on installation, with future adjustments via the barrel adjusters, so the distortion won't matter. Try setting the cable as follows.

1- bring the adjusters all the way in so you'll have their full range available for future adjustments.
2- holding the brakes closed, tension the cable and clamp it firmly.
3- squeeze the lever a few times to seat the cable heads and housing.
4- hopefully that gave you some slack and the brake is set fairly decently so only a turn or two of the adjuster is needed.
5- if the brake won't open enough, loosen the clamp slightly and gently squeeze the lever to slide come cable through then re-tighten. This is a feel thing and gets easier with practice.
6- if the brake is too open, needing more than a turn or two of the adjuster, loosen the clamp and start again, but you can skip steps 3 & 4.
7- tighten the clamp nut to final tension. Don't overtighten and break the screw.

8- BTW, never cut the wire until everything is finished and you're happy with the job. Then cut leaving about 1.5-2" excess beyond the clamp, and slip on a crimp if you like.

the really good brakes have small trenches cut into the cable clamp and don't crush the cable as badly.

That is the key, cables are cheap, and designed to be crushed. Live with it.

hmmm i like these barrel adjusters... i've never had brakes with them... or rather where they werent rusted/fused solid.
Maybe I need new brakes.

Hmmm im making another bike that seems to have 2 sets of barrel adjusters (upright levers + caliper brakes) when the norm seems to be 1 (upright levers + vbrakes OR aero levers + calipers). Can I use both and just adjust the cable rarely?