How many items and folders can be shared per account?

For both Everywhere and Business there is no limit on the amount of items that can be included within a shared folder.

For personal accounts with an Everywhere license, up to 50 items can be shared individually at one time.
Everywhere accounts also get up to two shared folders per account.

For Business accounts, up to 200 items can be shared individually at one time.
Business accounts have an unlimited amount of shared folders (Groups) per account.