I fretted the first fret, and then the 24th on my guitar. There was some space between string and frets on the middle of the fretboard. Not much, couple millimeters.

Does this mean i should tighten the rod a little?

Concerning the other problem with my intonation earlier. It's just my b string anymore, completely crazy Harmonic seems to be ok on the 12th fret by my tuner, but for example G on the 8th is off! Noticed it again when bending g10 whole step and compared it to b8.

Every other string is ok, quess i have some problems at my saddle, but this makes transcribing and playing guitar almost impossible, it sounds awful.
Ok, it's more than that, i would say about 2-3 mm, have to adjust it then! Thanks for the info. Iäm just getting into maintaining guitar's. I've just played them before.
Great. You Tube has plenty of videos on guitar maintanance, setup, repair, building, playing, etc. The info is out there to help you grow. Good luck..