Based on past Sofirn group buys:
1 - Sofirn has stores on AliExpress and Amazon. AliExpress sometimes takes PayPal and sometimes doesn’t, and when it does they usually charge a small fee. I always just use a credit card on AliExpress. Their credit card processing via AliPay is totally fine in my experience. On a side note, I always see new people treating AliExpress shopping as if it’s a daunting experience - it’s just Wish but without the markup.
2 - China. Overseas sellers will eventually get it at a markup. YMMV if you order it with batteries included.
3 - Shipping is usually free due to the Chinese government subsidizing shipping on packages below a certain weight.
How much will it slide now? All the weight is hanging down, so it will center itself on the bail (thank you for learning a new word :D).
I don’t see it sliding around much, had DBSAR tested this before?
I have many lanterns with the metal hoop-type bail, i never really had much of a problem with then on nails or cords. (unless you try to deliberately hang it on one side on something grippy like a rubber coated hook, they mostly center themselves. adding a protrusion will have it stick out (like a protrusion) when the bail handle is down though, and probably more of a hindrance when packing it in a a soft bag or case.
It seems that you will have to drill one hole vertically on both side, to meet the existing horizontal drilling made for the bail, if you need the paracord to go through the top part.