Unless it's changed since I last set up W10, it will ask you for you for your Microsoft Account and if you don't have one invite you to create one. If you have one or want one, fine, but you don't have to; in this house we're running W10 with local accounts, in the old-fashioned way. But you need an account to access the Store and some programs (and browser addons) have to be loaded from the Store.

Be aware that there is a version of Thunderbird in the Microsoft Store but the T'bird maintainers don't know anything about it (ref), so avoid it and get T'bird from thunderbird.net.. You can certainly move T'bird mail files from machine to machine, both whole profiles and mail folders - plenty of info online. If you're still using POP then I would bite the bullet and switch to IMAP.

If you, or anyone else reading, uses addons in Thunderbird, be aware that it is dropping support for a lot of old addons* - many don't work in TB60 and more will fall away with TB68 in a couple of months. New versions of many of the most useful addons will appear eventually, I think, in addons.thunderbird.net but the situation is currently a bit confusing. I've updated some myself - e,g. Use BCC Instead (which has been discontinued by the original author). Others have updated versions but cannot publish them until 68 is out.

*This has been forced in them by technical changed to Firefox; there is a lot of Firefix code is in T'bird.