Glad you joined! I've learned a lot from this forum. Wishing you all the best on your upcoming cruise.
I'll try to answer regarding excursions.
I wouldn't wait on Alaskan excursions this year. They are selling out fast. If you see something still available you'd like to do, book it! You should be able to get a refund from almost anyone (cruise line or not) if you have to cancel due to covid. Just verify before booking. Some excursions may be available through the cruise line after boarding, some might be available at the pier, but I wouldn't risk it with Alaska. I'd book now.