...everything?!
Before I give my suggestions, I want to know how long you expect this to take.
For starters, I recommend looking at the Dojo and especially Smashwiki (probably one of the best and most constantly updated for general information), as well as checking for constant updates.
I recommend that you emulate the SSBM "Official Everything Thread" written by Uncle Kenny:
http://smashboards.com/showthread.php?t=97603. Enough people would be happy with that.
It would be inefficient to put everything into one guide: There are a
LOT of pages in all those guides.
Character Specific would be very painful to accomplish, for example.
Do not forget that since the SSBB metagame is "low-tech" right now, there will be MANY updates to keep up with for each section. In fact, there will probably be updates for everything for a long time.
In the end, I recommend putting off this project, or at least several pieces of it, for another couple years. There are too many things big and small to keep up with right now. Or, if you really want, you can make several links to all things Brawl or just concentrate on a specific area, such as competition.
For now, I guess move sets are OK as far as I know
Seriously, unless you copy/paste with permission or make links, this task will get complicated.
Good luck, and I would like a PM if you actually complete the guide.
Edit: Define "Almost Everything." For example, what about frame rate data for each character?