Edit History

Prestashop 8 wasn't such a huge leap to be honest (it was more to mark a new "era" for Prestashop) and your payment modules *should* work just fine if they have been properly written and maintained. You can always check with the author for updates. You might need to update your theme to support the new password policy (if your theme is remotely based on the classic theme then it could be a minor change for you by merging changes from the new classic theme. I would recommend using a tool like WinMerge to assist in updating a theme).

It is also very much worth setting up a local staging environment and then doing the upgrade to test, of course!

Changelogs
https://devdocs.prestashop-project.org/8/modules/core-updates/8.0/
https://devdocs.prestashop-project.org/8/modules/core-updates/8.1/

New password policy
https://github.com/PrestaShop/PrestaShop/pull/28127/

EDIT: You also need to check that any third-party modules you are using in your store support php8+ as well as PS8+. It should be fairly easy for module authors to upgrade compatibility.