Can back up / restore for a hard reset on Galaxy Note be done using Samsung Kies?
The KIES backup/restore function should work, as you are not rooting, upgrading or changing ROMs.  However, it can be a little flakey, so be prepared for this to not work and to lose your system and app settings.
See 1.
A reset certainly won't harm it.  However, lags are likely to be due to one of your apps misbehaving, so a backup/restore will likely put you right back in the same boat you're in now.