My Mac is so slow.

if you think your slowness is related to some software that you have installed, i would avoid bringing everything over, and instead manually move the data you want to keep to some form of external storage. then after you complete a fresh macOS install, you can manually move the data from the external storage back onto the mac.

Are the Photos and Document stored on a Cloud Service?

Is the e-mail account used using the IMAP Protocol ?

If Yes to Both questions above - once the Start Over is completed all three category should be available again privies the Same Account is used again.

Personally, would perform A Time Machine Backup before hand.

For additional purposes - For addition purposes - two Tested Clones each to separate external drives. This is insurance incase.

EDITED

Set up iCloud on all your devices

Apps and features that use iCloud

The two above pertain to the Photos specifically and some other important iCloud functions

As for Mail On your Mac Folder - one can Export the e-mails in a format like PDF and then move to a safe External Drive

At most any office-supply store, you can find external hard-disk enclosures which attach via USB or USB-C. (Even if you buy one that has a hard-drive or SSD inside of it, you can temporarily remove it.) You just need to look at the drive in the old Mac and see what kind of physical connection it uses. Now, you can place that drive into the enclosure and mount it on your new Mac.

(Yes, you can even buy enclosures for "original SCSI ...")

Note that "file ownership and permissions" can be a bit of an issue since these relate to user-id and group-id numbers which might not be the same from one machine to the next. But these issues can be dealt with.

From personal experience, and have had many Apple Computers over the years.

When I have Reformatted the Drive to Zero and reinstalled new, whatever was on iCloud was there again including all Photos

You are welcome and thank you too 😀

Do come back to the Apple Support Communities ( ASC )  in the future, if / or when additional questions may arise