New MacBook Pro iCloud syncing concerns

Hello! I am purchasing a new MBP today, so that I can separate all my personal documents and files from my work laptop. I should've done this long ago for security purposes. Most of the content on my old MBP (for work) is my personal photos, documents, etc...As such, once I migrate everything from my old MBP over to my new one, I want to make sure that the OLD laptop doesn't override my NEW one when syncing to iCloud, since I'm going to clean off all my personal files from my WORK laptop. My initial thought is just to disable iCloud on my OLD work laptop, and just keep the files I use for work on that one. Maybe I can still sync Contacts (since many are shared) and Mail, since I'll want to be able to check email on both devices. But other than that, I don't want my personal info on the OLD work device. I'm NERVOUS I'm going to lose something when making this major change! I will clone my hard drive on my external drive before making the changes, but I just want to do it the right way and not cause hours of headaches or confusion - or worse yet, losing important documents or photos by my OLD laptop talking to iCloud once it's cleared of so much. Does that make sense? I'd love some advice! Thanks so much!

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