3000 or 4000 notes allowed inside icloud? a single note maximum bytes?

At present, you would be restricted to the amount of storage space you are actively subscribing to for iCloud. Say you have a 5gb account, well then you can store 5gb worth of notes and attachments inside said notes. Once you reach that threshold, you wouldn't be able to store them to iCloud any further. But, speaking from a personal stance, if you have that much in notes content, it might be best to back them up to a secondary source once in a while, because iCloud notes are a syncing service, not a backup. Delete something and its deleted from all devices, and if you empty the trash, its gone forever.