Is using a Mac mini as an iPhoto server for 2 client laptops a good idea?
You can happily place the library and have it share out.  You will need to have iPhoto running at all times in order to have the library visible to other users tho.

When you connect to the library from another Mac, you will not be able to use the same Events/Albums views that you have locally.  Some of it is available, but mainly it just throws a huge list of all your stuff that is not organised in the same way as you would expect if it was local.  Also, it's SLOW, in that it seems to almost cache the contents each time you connect which can take a while, and subsequent navigation is not quick either.

Another way to do this, is to share out the folder that the iPhoto data resides in, rather than opening iPhoto and sharing your library via the app.  This has the advantage that iPhoto does not need to be running on the Mini, although the disadvantage is your Apple TV won't connect.  This will however open the library in the same way as if it were local (in essence it is local, just on a network drive).  You can test this out by holding OPTION down as you start iPhoto, it will let you connect to a different library.

All in all, it's not a great solution either way.  I long for a sensible way of sharing in iPhoto and iTunes that does not require the apps to be running at the time (just a background sharing daemon would be great), that allows you to navigate and modify as if they were local, but it does't really exist for either app, and any solution is substandard to your local install workflows.