While it's not a 'Real' M14 the M1A is a good rifle. Also, as
mentioned, at 100 yards you won't tell the difference between a Standard and a NM except for the weight.
Cleaning and disassembly; Clean it like a Garand. Turn it upside down in a gun-cradle, clean the bore and the Chamber. Reason you turn it upside down is you don't want solvent getting into the gas system. While the M14 Platform uses the 'White' Gas-System instead of the long direct impingement system of the Garand, both are supposed to run dry. Tear it down once a year for a good cleaning. That's all you'll need, you don't want to take the action out of the wood anymore than absolutely necessary as each time you do it loosens the wood and you lose a bit of accuracy. Like a Garand, a good tight-fitting stockset is almost 60% of the accuracy-level in a M14 platform.
Yes, you can shoot 308Win. in a 7.62NATO chamber,however, you will stretch the cases a lot so, reloading will be iffy. See, a 7.62NATO chamber is larger than a 308Win. Chamber. A 7.62 chamber that almost closes on a No-Go headspace-gauge will swallow a 308Win. Field-Reject gauge. While the two rounds are the same size dimensionally, the military 7.62 chamber is made larger for reliability in adverse conditions of Combat. Further, while the same size, 7.62NATO brass is thicker than 308 so, it doesn't swell as much in the chamber.
The good news? 7.62NATO, from what I'm told by shooters I know over in Europe, is fairly plentiful. You shouldn't have any trouble finding ammo for it.