Every each account has its own quota limitation (up to the account that you choose).
The users that you will create to use this account will share the total amount of space that the account has.
In case that you choose that one/multiple specific user(s) of yours should have their own specific quota inside the initial account quota - it is possible.
All that you have to do is to write email to firstname.lastname@example.org or send a ticket to Transferum and make such a request.
The quota allocated to each account can not be exceeded. If you need for your account more space all you have to do is delete some old useless data or request an update of your Account.The update can be done at any time with no impact over the service.