What do I need to do in order to integrate Kolab into my favourite Linux distribution so that I don't have to use OpenPKG?
This is no easy task and you definitely need good development skills in addition to a good background in configuring mail servers. Read on here.
Can I build the Kolab Server from the Kolab CVS code repository?
Yes, this should be no problem. It is the best way to test patches you developed yourself. The necessary instructions are here.
Can I create my own Kolab server release?
While this requires a good deal of knowledge about the server you can certainly do so. Some information on building a release can be found here.
Why has the Kolab Format been developed instead of using already existing formats?
The intention of the Kolab format is to define a small set of features that will be supported by all Kolab compatible clients. Most available formats do not have cross-client-compatibility as a primary focus. Further details are discussed here.