macOS Catalina, macOS Big Sur and Windows 10 - Triple Boot Plan
Cause any issues with iCloud Music and iCloud Photo libraries as I will use them on both macOS Catalina and macOS Big Sur?
No.

Jeopardize my Bootcamp partition in any way?
No.

Allow me to reclaim the space used by macOS Catalina currently so when I remove it I can allocate that space to macOS Big Sur?
No.
I would suggest one of the following two alternatives.

Use the Disk Utility to add a new APFS volume in the same APFS container partition as Catalina, then install Big Sur to this new APFS volume. Later, you can use the Big Sur Disk Utility to delete the Catalina volume group.
Boot to Catalina macOS Recovery. Use the Disk Utility to create a new APFS container partition. Enter the same name use by current Catalina. Next, use the Disk Utility to restore (replicate) Catalina to this new APFS container partition. Quit the Disk Utility and then choose →Startup Disk… from the menu bar. Choose to restart from the replicated Catalina. This would be the one that is not initially highlighted. Use the Disk Utility to erase the APFS container partition with the original Catalina. Enter a name for the new APFS volume where Big Sur will be installed. Next, quit the Disk Utility and install Big Sur to the new APFS volume you just created. If necessary, first download Big Sur from the App Store. Later, you can remove the APFS container partition with the replicated Catalina and merge the space back into the APFS container partition with Big Sur.


Any other issues?
No.
However, user user3439894 has suggested the following popup message could be an issue. This popup may occur when booting Mojave on a Mac with Mojave and Big Sur installed in either the same or different APFS containers.