Hi, I've got a serious case of Flash-hound fomo I love this doggo skin, The armour the sword the potions it's my perfect companion pet!

I know that purchasing a pre order pack unlocks add-ons up to that level and I know I can upgrade my pack to the highest tier.
My Question is
Can I buy multiple monthly packs at different tiers or are you locked to one pack plus add-ons?
If I buy the Thunder at the Gate Expeditionary pack for $150 today can I buy a full voyager plus pack for a
different set later will the embers and game time stack?
Thanks