Hi klokwerkaos,
If you create your account on the page which was opened from the software when the Tutorial was completed it’ll already have all the necessary account information to perform the account linking in the background, however, if your account was created at a later step, you’ll need to manually link your accounts, which is an easy process and only involves a few steps. You can find guides on how to do that on our site:
All Achievements are tracked separately, so you can buy the Season #1 bundles in a single transaction, and unlock all the free packs for the First Buy, Season #1 Completion, and the Pro version Achievements.
I hope this helps, but let me know if something still doesn’t work. 🙂