#2
All laminated, so likely durable.....As to the sound....Only you can judge.
NOTHING will "stay in tune" indefinitely. Save a few bucks for a cheap electronic tuner.
#3
If you have tuning issues, lift the strings, take a pencil and draw the lead through the nut and bridge slots so they're coated in graphite. If you're still having issues, buy a cheap set of locking tuners (you can pick up a set of locking Sperzel's for around $50 from Stewmac) and replace the old ones.

Also take the time to make sure you're stringing it correctly. You'd be surprised how many times I've fixed people's tuning issues just by showing them how to properly string their guitar.