I have almost the same setup as you have but do want to double check for improvement and the use of autostream.
All photos are stored on an exHD, using autoimporter that i found in the iPhoto package in the pictures lib. If I connect a camera or iphone autoimporter nicely adds tags to the directory with name of the camera, date, etc. really great. Once this is done i drag-drop import directories from the exHD into iPhoto without copying the photos to the iPhoto lib not to copy all photos onto my Mac. Its about 120 GB now and growing and i want to keep my Mac clean.
Almost - not really - choosing not to copy the photos is a major problem waiting to happen - at this time no experianced iPhoto user would make that choice - it makes importing and deleting more complicated and makes upgrading hardware or replacing defective hardware very difficult to impossible
Question 1: can the import function from an exHD into iPhoto be automated, meaning that new directory or photos are being auto-detected and the import takes place automatically?
Not using iPhoto - there are third party programs taht can do that as can automator
Or should i move the iPhoto lib completely to the exHD. What does this to speed?
That probably is a good idea - as to speed that is totally dependent on the connection - with USB2 or 3, firewire or thunderbolt there is no speed problem
I also have AppleTV2 on which i want to use photostream. My goal is to make a picture, enter my house, its auto uploaded via wifi into iCloud and through photostream, and i can see it on AppleTV2 right away.
But i found out that i only can see photos on AppleTV2 if imported into iPhoto (is this correct?)
You can only use PS from a device that supports PS, of course - so to place a photo in PS you must use an IOS device or iPhoto
Question 2: How do i combine both goals: a) keepng my Mac clean by using the exHD end b) being able to see pictures on AppleTV2 enjoying the auto upload though wifi+photostream once entered the house.
Moving the iPhoto library is safe and simple for managed libraries - very difficult for referenced libraries like you apperantly have so there will not be an easy solution - with a referenced library you simply quit iPhoto and drag the iPhoto library intact as a single entity to the external drive - depress the option key and launch iPhoto using the "select library" option to point to the new location on the external drive - fully test it and then trash the old library on the internal drive (test one more time prior to emptying the trash)
And be sure that the External drive is formatted Mac OS extended (journaled) (iPhoto does not work with drives with other formats) and that it is always available prior to launching iPhoto
And backup soon and often - having your iPhoto library on an external drive is not a backup and if you are using Time Machine you need to check and be sure that TM is backing up your external drive
Once you have imported photos to iPhoto you can drag them to PS or you can use home networking (turn on in iTunes) so the Apple TV can see your iPhoto library directly
LN