This is something you would really need to contact your host about first to get some more information. In particular to find out what resources you are running out of and why. Then some recommendations on how to improve that could be provided. There could be many things happening.
For example, if it is a storage problem due to the dynamic CSS then this will be greatly improved in 5.6. In 5.5.2 if you have file mode set for the dynamic CSS compiler than will mean a separate CSS file for every page (in your case 20k+). In 5.6 that has been changed so the CSS files that are stored are only stored separately if the styling is actually different. in the vast majority of cases they will be the same. So instead of 20k+ there is likely to be only a 20 or so, depending on usage of PO.