Can sprockets and track nuts be overtightened?

I read everywhere that you should tighten the sprocket as hard as you can. Is there a possibility of over tightening it and threading the hub?

Same question for the axle / track nuts.

it usually takes quite extreme force or some cackhandedness or a combination of both to strip sprockets / nuts
that said some hub manufacturers have less good quality alloys and lower quality control so might be easier to strip

The answer is yes to both all threads will strip in enough force is used.
Fixed sprocket, do it up as tight as you can by either a chain wrench or riding the bike with the lock nut off and standing on the pedals as hard as you can, stop by using the brake and then put the lock nut on.
Axle will be much easier to strip the thread, so use the spanner of the correct length for the nut provided you do not use all your strength to do the nut up you should be fine or you can use a torque wrench set at the correct figure for the size of thread. Doing nuts and bolts up is like a lot of things in life you learn by experience.

Coppaslip on the the threads is good idea to help getting them off.

It's coppERslip. CoppERslip. And it's fucking minging and shouldn't be put near a bicycle.

A bit of standard grease however, will allow you to get things tighter and will also aid removal.

In the case of cog and lockring, much more likely for damage to occur if not tightened enough than it is for you to over tighten.