Awesome. I started watching wrestling (well, just WWF) in February 1999 when I was a kid, so I have a ton of nostalgia for the whole '99 to early 2000s era.
I've always been interested in what WWF would have been like if Steve Austin didn't get injured in 1999 (which led to The Rock stepping up as the next big Babyface in 2000). Personally, I think fans would have gotten sick of Austin's gimmick and constant wins, but that's just me.
For realism's sake, you could make sure The Giant's WCW deal expires after January '99 (technically his last appearance was February 8, 1999), and Chris Jericho's WCW deal expires in Summer 1999. The exact date of Jericho's contract expiring is iffy because they kept him stuck to house shows. According to Wikipedia, he signed with WWF on June 30, 1999, but his last WCW appearance was July 21, and he debuted on Raw on August 9.
Again, just a suggestion for realism's sake. Giant and Jericho jumping to WWF were pretty big turning points in the Monday Night War.