For a Windows 98 computer a 500 MHz Pentium III will be a fine CPU. The Celeron lives firmly in the Windows XP era.
With something like a Voodoo 3 you'll have a fun time playing older games like Quake II and III, Unreal, Unreal Tournament, The Sims, Sim City 2000, Warcraft II, Duke Nukem 3D, and a heck of a lot of other games.
I remember playing all kinds of very fun games on my K6-2 500. Man, I love playing those old games and I really miss having the original hardware I played them on. I had an S3 Savage4 video card at the time, and the S3 textures on Unreal Tournament were outstanding. There were a few other games that supported the S3. However, there were lots of games supported the Voodoo 3DFX Glide.
A Sound Blaster 16 is a pretty good card for the time. It is what I used and it sounded pretty good. Great DOS support too. It was just about the standard for the time.