What power should I sign up for?

Depends upon the characteristics of the equipment that you have installed in your business or office.
By way of guidance, the capacity that you're going to need can been optimised by adding the capacity of the highest consumption receiver to the others that are to be used simultaneously.
The power contracted must adapt as much as possible to the power that you will need. If the power contracted is insufficient, there is risk that a fuse will be blown; on contrary, if the contracted power is excessive there is a possibility of incurring an overrun.
You should also be sure that the installation of your business space or office is prepared to allow for the functioning of your equipment.
In the Electrical Installation Certificate (CIE) or Bulletin, your installation's principal characteristics are given such as installed power and maximum admissible power, along with provision of a guarantee for the installation's quality.
In the case that the power that you need is above that admitted (which you can see in the current bulletin) you should get in touch with your electricity installer so that a new bulletin may be created. Likewise, if in the future you change your power needs (for example, because you install new devices) you may need to update your installation.