- is there any preffered profile and where do I find it?
No, there is no profile.
- would it be suitable to include that in the tycho-setup directory?
Yes, but what's even more important if we want to enforce/encourage a formatting is that the .settings/ of all modules do reference the same formatter and enable some format on save actions.
Actually, we could stick to the default Eclipse formatter that's built-in (so we wouldn't need to share it) but just ensure we enable this formatter in .settings/
- should I always format the whole file or only edited lines?
I don't think it's important enough for project perspective to make chose one or the other. In general, it's up to the developer to do what's best for them, they're trusted to do the right thing and the project doesn't force a workflow or another.