Use Cloud library Sync to switch to a new Macbook

Is this assumption right ?

Yes

What if I edit playlists or add new songs on new playlists is it also being updated on my old Macbook in case I will need it ?

Yes, just make sure you give it enough time to sync

Who has experience with this ?

I tested it when I was using a dedicated PC and my Macbook Pro. 

What about the Creative plan VS Proffesional Plan

What about it? There are mainly 2 differences.

1. You get unlimited storage with Professional
2. Auto sync for any track that is imported into your collection/library with Professional. 

People complain about the price of the Professional plan but forget that if you are set up as company/freelance it's business deductible. 
It's mostly attractive for those that want a 'Set & Forget' workflow. 

@Pulse is it not easier with the cloud sync to move the database from my Old Macbook to my new one ? My original tracks are not in just one folder but in different folders... 

@Arian > File > Library > Backup Library. During that process, say "Yes" to backing up the music as well. Move that backup file and the folder full of consolidated music to the new computer, where you go to File > Library > Restore Library and all will be put into place.

This Back-up with music as well, it will be very big right? You need to have your backup desination to be big enough. In my case, I need to buy bigger a bigger (portable) SSD. Deduct this too from your pro plan subsciption and it becomes more attractive.. 

@Pulse To me it feels safe to have a auto-backed up library in the cloud because hosted only on a local device it can get lost, stolen or damaged.. and needs back-ups. Why do you prefer a local library instead? 

Only question I have: what will happen to the Cloud library/database when you quit or change your plan! ..I assume you get to keep your hot cues/loops/saved cues/grids/phrases/lightening edits/matches etc. Am I correct? 

I use the external SSD to store my collection, but keep a second copy on another SSD, plus a copy in Dropbox, and another in Backblaze.

I prefer local so I can move it from computer to computer without need for an internet connection.

If you quit your plan, so long as you have all your music downloaded out of the Pro plan, or you pay to keep your Dropbox storage in the Creative plan, your library within rekordbox still exists locally - that doesn't go away, it just no longer synchronizes to the cloud / other devices.