Freeze Egg Yolks?

If you whisk in 1 teaspoon of sugar per egg yolk it'll keep the water in the yolks from crystallizing as much, you'll get a better outcome. You just have to remember to exclude the equivalent amount of sugar from the recipe you end up using them in.

Certainly. Just be sure to whisk them together first, and when you make the custard at a later date, after cooking it, be sure to strain it. Freezing toughens the membrane around the yolks.

Yes. No problem.