Hi Mark!
I don't add sugar or salt to my spices, as that limits how I can use them later. If you put salt in several herbs, then want to use all of them in a dish, how much salt do you now have? So I leave mine plain. I cap them tightly, and have no issues with them.
As for when you can strip herbs, I'd say (and I'm NOT up on your climate, so I don't know how the ones you have will behave there) to not fully strip any that will hold the leaves over winter, leave them some leaves to support their growth in spring, since they expect to have leaves. Anything that will drop their leaves, harvest them a week or two before they will start dropping. Some herbs are happier if pruned to the ground, any that are like that, take the whole plant, again, a week or two before the leaves drop. Annuals like basil I leave some for seeding, and take the rest to the ground before the seeds start forming. Seeds use a lot of a plant's
energy.
Happy herbing!! I was amused to see this post as I am sitting here eating breakfast, bad stomach day, so just pasta with butter and a lot of dried herbs :)
:D