Congrats on your first sale, btw! :)
I use flat rate priority shipping for US orders (with delivery confirmation, and insurance on orders over $150), but then my pieces are quite heavy. Yours look to be pretty light, so basing shipping on weight might be more economical for you. Just always always always get delivery confirmation.
Priority International is WAY higher than First Class International, so unless your customer asks for expedited shipping, I wouldn't offer it. I do make that offer in my policies and request that customers convo, but so far no one has. I don't know if that's because no one has needed it, or no one has read that I offer it.
For the holidays, remember to put in your announcement when the last day you can take orders meant to arrive for Christmas. I'm still trying to figure out the exact date, but I know it needs to be done.