I understand that Photostream can only be linked to one library at a time. Does Aperture solve ths problem? I have not purchased Aperture yet, but I will if it can solve my problem.
You can only have one photo library sync with the Photo Stream; that is a feature of iCloud and independent of using iPhoto or Aperture.
You can continue to use the Photo Streams you set up in iPhoto, if you switch to Aperture - if your iPhoto version and Aperture version are compatible, you can use your iPhoto library with Aperture.
. I want to spilt my libraries up, because my single library of 30 000 photos is running quite slowly, however I wish to keep all my current photosreams live.
Slowness of iPhoto or Aperture is usually not caused by the size of the library, unless your system drive is dangerously full and you have not enough free working space left on your system drive. How full are your drives - less than 10GB space? And where is the iPhoto library located? On an external drive or the system volume? If external, how is the drive connected?
Have you tried if repairing the library will help? See: iPhoto 6 and later: Rebuilding the iPhoto library
I'd try the repair permissions or repair database first, before going for a full rebuild.