#2
What type of guitar is this? Neck can always be repaired, even if its twisted (not badly twisted). You could re-sand the fretboard and oil it up with bore-oil, get it leveled, re-install a new nut and so on.
"Play with your ears" - Yngwie Malmsteen, Paul Gilbert
Thats what she said...
UGmusic
#3
About the buzz, you have to adjust your neck with the small screw which is on the head.
About the fret deteriorated, you can call upon a guitar maker or a music store but I've ever heard it's so expensive.

If you want to change your neck, you must buy this part (approximately 100-150$ for an occasion) and you may have to call your guitar store to adjust it (I don't the price but it may be 50$...)
#4
mmmm check your neck warp cos that could explain the buzzing at nut. also you could re-fret the neck which is for those that have a set neck, set-thru neck, or neck thru