One thing we have to define: Who will be the beneficiary when closing down the e.V. for whatever reasons? So basically, where does the money go to in case the e.V. stops existing.
Suggestions from my side:
KDE e.V., because they helped us to get started by hosting our initial mailing list
FSFE e.V., because free software is essential for a privacy respecting world
MyData , because they are doing the lobby work for a privacy respecting future
Right now - and I know things can change - there would be no role for the e.V. once the Stiftung has been established. So, I guess no.
The Stiftung will have a business model grounding in its function as a trustee for users. We should be able to pay people working for us, not asking for money as Stiftung.
While we are still a Verein, relevant “Vereinsbeiträge” would need to be so large in order to bring any effect, that it again does not make sense to even start with them. We will need voluntary work and where this does not work out funding (e.g. Mozilla or Prototype Fund) to pay for the work being done. I might ask at some point for some donations in order to cover the involved legal costs for establishing the Verein, but cannot think of anything else really.
MyData is more an industry thing, and as far as I know well enough financed by that. From that perspective, I think FSFE or KDE would be better beneficiaries.