This will be the last email from me to LUV on this topic so as to de-clutter peoples in-boxes. Anyone interested in further conversation please feel free to suggest a way to do that. I'm thinking to just create an group within my contacts to keep people posted, but better suggestions welcome.
 
BTW: Owncloud is interesting, as the central storage of files.

Good tip thank you.

And then a database..

A lot of stuff comes per e-mail. But I have a problem to link it in a
database because it is lacking a URL, a unique ID and a way to access it
via web browser.

(E.g. "Project organizer, e-mail by Scott Junner -> read original e-mail")

Well, there may be a way to fetch all your e-mail and store it in the
database. But it seems to be so "disconnected" to the reading of e-mails
(which can be everywhere, of course) so it feels rather clumsy.

Any ideas to solve this in a elegant way?

I'm now berating myself for neglecting to see this one for myself. That is so important. Thank you for expressing.

I have worked with an enterprise level application (as a user) which linked to emails. Have made a note to contact the company I used to work for to get the name of that and see if it I can look deeper into how it was achieved.

One thought is to make use of a number of pre existing online applications. Google calendar, tasks, contacts, gmail and perhaps evernote and dropbox. But that starts to smell a little too much like my own personal situation and not something which can be easily shared without forcing people to open accounts with services they don't want to. On the other hand it might be a great way to prevent a whole lotta work.

There are so many things I don't know about here and that's kinda why I want to try, so I can get to know all the stuff I don't even know I don't know.

Scott