I'd recommend you leave the events as is - collapse the section if you want. Events, by default, are created for each day photos exist on, you may find it useful to refer to these at some point. You may find it helpful to rename events - Sally 10th Birthday, Halloween 2009, etc.
Use Albums, and / or Smart Albums for your organized photos. You are not creating copies of photos when you place them in an album, you are just creating a link in the album.
With 25k + photos I would also recommend folders to help keep your albums organized. A common approach is to create a folder for each year, and possibly subfolders for each month. I do folders for years and put albums into those.
If you have 25k photos, you're probably a pack rat. I recommend you get rid of the duplicates, the horrible shots, and even a lot of the good ones - just keep one or two representative shots from each event. NO ONE, not even you, really wants to look at 25,000 photos. If this is too painful right now, try just creating a Delete Candidates album.
If you find you like Smart Albums but want to tweak them a bit, create the Smart Album, then create a standard album. Select all photos from the Smart Album and drag them to the standard Album. Then add or delete from the standard Album as desired. Delete the Smart Album if desired. Obviously, the standard Album will not update automatically.