How many users can I have in each plan?

That depends on the pricing plan you choose.

The Free plan is limited to 2 users, while both the Team and Enterprise plans can support an unlimited number of users, however, the monthly price will depend on the number of users added.

Both of the paid plans offer: file attachments and unlimited boards. Additionally, the Enterprise plan will give you access to some exclusive features.

You can manage your plan setting in Account Administration - Plan & Billing Details.