Unless you are going to have many many portal sites and each one has a great amount of data, I don't think you will reach anywhere near 100GB of space.

If you are really going to use 100GB of space or 100GB of data transfer, that would mean your portals are very busy sites and there is a good chance that your account will be suspended / shutdown for excess memory or CPU usage.

There is a limit of what a shared hosting account can do as the server resources are shared by a number of other accounts too. It is very unfortunate that hosts have used massive overselling adverts which has now given end-users false impressions for what they actually need and are actually going to get for the amount of money they are paying.