Hi Lukas,
Seems to me that investing more time diving deeper into requirements analysis up front will be enormously helpful in guiding the selection of a specific solution platform, related tools, and implementation and maintenance methodologies. So many questions come to mind, off the top of my head ...
* security and governance policies: over the wire inside and outside firewall, information access: what, when, by whom, how fine-grained (page, document, element levels?); who maintains customer employee accounts, employee accounts; security-trimmed UIs?
* CMS - for what primary purposes: comprehensive EMC with e-discovery? more publishing and maintaining web pages? page-oriented or element-oriented? primary types of digital artifacts (HTML text, movies, images)?
* Assuming CMS primarily for web publishing purposes, what workflows to implement? (authoring, editing, SME review, final pub approval, publication and take-down dates, versioning)
* What metadata will be developed and maintained throughout published pages, documents and other artifacts. Controlled vocabularies, taxonomies, folksonomies?
* What kind of documents (Microsoft Office, PDF, other?). Need for read/write access, versioning? Need to track access, restrict access? * *
* Who will upload documents?
* Search? Security-trimmed search?
* how many total users?
* how many concurrent users now and in foreseeable future?
Answers to these and other questions involved in a more rigorous examination of your client's needs (both stated and, sometimes more importantly, not yet articulated) can better inform some key strategic decisions: make or buy (i.e., engage a consulting firm for open source or consulting and licensing fees for proprietary? if buy, cloud or self-hosted? what platform? platform out-of-the-box capabilities and learning curves for you and your client.
Just some thoughts.
Best success,
Brian