before game = 1800 won't work, because TD doesn't recognize it as that. You want it to be conditional, state=1 for example. I don't know for sure what you'll need for it, but i know it is state. If the tournament starts shortly after the registration closes, why not combine the two - "Registration is now closed, and the tournament is about to commence"? I would think that would assist on preventing the overlap.
Countdown with 2.5, you are correct, you need to have two people in. But if you use the beta version, you can start it immediately, and have the tourney not start at the end also.
Clashing - I believe somewhere in the preferences you should be able to control that. Not sure if it's from the preferences tab, or from the Events tab preferences button.
(Presently at school, not at laptop).
Hope this helps you out some, and sorry I couldn't be more specific.