Ok my 2 cents worth.

I personally prefer buying from the arena first, ebay second and then facebook. As a seller it's properly better to sell in the opposite order due to the pace ponies move.

I don't think shipping methods matter too much, people will pay it if they want the ponies. I prefer to buy the cheapest tracked method available.
As a seller, I would only recommend tracked shipping as there have been so many horror stories with shipping since covid started, you want to be covered.
I would offer to US buyers first then only if you need to, offer to international buyers. I only say this as most international people can send to a usa forwarding agency so they are still able to buy for you and it saves you having to get intl postal quotes.

Packing - personally I am not fussy, plastic ponies are resilient! Just make sure the material wont transfer ink (newpaper, plastic with vivid on it). I also prefer light weight (bubble bag rather than box) and in a sized bag/ box to fit the purchase. I use a forwarding agency and we get charged on both weight and dimension of the parcel).

I would single out expensive ponies (over $25+) and sell individually. Depending on how fast and easily you want to clear out ponies I would bundle common ponies and throw in one harder to find pony so people will buy the lot just for the 1 htf pony  I wouldn't split the lot as you will be left with ponies.

I buy ponies singularly or in lots I just use paypal  I love add ons I think everyone does, I display pony art with my collection 

I don't normally get extra insurance, I feel secure with tracking and just take my chances

I haven't posted to canada since covid but even before the pandemic parcels would take 9 weeks or so to arrive in canada, parcels anywhere else in the world would take 2-3 weeks.
Post to canada in my experience and alot of other kiwis experiences have taken forever. The good news is that all arrived.
I wouldn't be too paniced yet if I were you, I do understand how unsettling it is thou! I think it will arrive in the next few weeks

bumping have added a few more ponies to the list

I think $90 also

B all day long

I still need to get this lady, I have the variant haired version of her thou

bump