New Scotch Lover, A Few Questions

Hello everyone,

I've been getting into single-malt scotch for the past half-year (as long as I've been legal), and have already acquired 5 different bottles from different regions because the variations in them are fascinating to me.
I have a few questions though, and was hoping for some help.
What is considered the "right amount" for a glass? I've heard everything from .5 oz to 2 oz. It's probably preference, but I was wondering if there's a "correct" amount.
Also, It seems like the taste of a scotch can vary enormously from night to night. Is this common? should I cleanse the palate before tasting?

Thanks!