I completely removed the dots in my "dev-N900" and in my "spare-N900" as well. But I've never documented anything I've done so far.

Looking at the dpkg list, there is nothing with "welcome" on it (although this is already known).

With "startup" I have:
hildon-initscripts
maemo-launcher
osso-af-startup
osso-startup-wizard[*]

As long as you don't touch any of the above, you can remove anything that has the word startup in it, most importanly: hildon-startup-progress
[*] Add.: funny. I just checked in my "normal-N900" and there I removed hildon-startup-progress *and* osso-startup-wizard (that's the one asking for regional settings and time when you take the battery out for too long). I therefore declare this operation to be safe

DISCLAIMER: I don't have the .deb with me at the moment, so I cannot look at preinstall, postinstall, etc. so I *may* have done something besides just apt-get purge'ing it.

But I really don't think so, so feel free to purge it.