1. Yes, it was early 90's, I believe it was summer 93 or 94.
2. Yes, Tracy was the PD
3. No, KYSR was first.
Here's some of the events as I recall them:
Jeff and Jer left B100 for Q106 sometime around 1992 or 93. There had been some ugly public events when they left. Tracy Johnson how had just let Magic Matt Allan from KIIS go wanted another big show to replace him, and Jeff and Jer had talked to him. There is also some indication that Jeff and Jer were unhappy with KFMB's insistance that B100 stay a Mainstream AC, despite expirementing with a more loose "Unplugged Format," on certain weekends. Eventualy, KFMB FM found out about the talks, and promptly fired them, claiming that it was a violation to talk to other stations before their contract was up. After that, KFMB VP and GM Robert L. Meyers (aka "the Colonel") read a statment on the air the day they were let go announcing the amount that the duo were paid in their contract. Jeff and Jer's firing (which was a suprise to everyone who knew little about the move) angered many listeners, hurting B100's ratings, especially a few months later when Jeff and Jer showed up Q106, and B100 was never able to recover (although 12+ remained decent in San Diego's North County, where Q106's singal had a rimshot reach).
I believe it was in early Summer of 1994 (or perhaps late May), after failed attempts to replace them with John Lander (now at WBMX Boston) and Jules Brandt, and then Larry Himmel, Tracy Johnson who had left Q106 with an entire staff to KFMB AM and FM, ran a stunt called "The Great Radio Experiment," where they played a different format a day for 3 weeks. After that, they launched Star at Midnight on a Monday morning (not sure of the exact date but I think it was in June). The new format was still Hot AC which was officially what B100 had been for many years, but the difference was in the presentation. In press releases, the new format was referred to as "Adult Top 40."
Unlike B100, where the voices would often backsell without a music bed, the new presentation was very produced, element heavy, and rarely had anything that sounded like dead-air. Before the major changes, B100's on-air staff consisted of Himmel and Brandt mornings, Gary Kelley in the Middays, "The Greener" Gene Knight afternoons, and Danny Romero with "San Diego After Dark" in the evenings. Eventually, Gene and Gary were let go, with Kim Morrison moving from Part Time to Middays along with Gregg Simms doing some Fill-in, and Danny Stayed for a short while before going to LA to do weather on KCOP (he had been doing some weekend weather for KFMB TV News8). Also Just before the "experiment" B100 had shifted their format to a Mainstream CHR for a few weeks, matching the music played by Q106 and even KIIS-FM, first using the slogan "Continuous Hit Music, B100," and then actually stealing "A Better Mix of Music and more of it" (a famous tag line form Q106, that was even seen on Q106 billboards all over San Diego). There was even a "Phrase that pays" contest breifly. Also, Dave Smiley did his show in evenings but was unable to speak (for contract reasons). Instead, he used many of his old sound effects from Q106 (and also answerd the phones and let callers proclaim that Dave Smiley was indeed "on the air," in addition to his famous "Real Wild One" sign-on song by Iggy Pop. All that changed when Star officially signed on, with a format a slightly more AC music selection then some might have expected (KFMB had hinted in the experiment that the new format would be a more risky Top 40 KIIS FM/MTV-like format than previously heard).
KYSR FM "Star 98.7" singed on in 1991 or 92 before Star 100.7, and was orignally much more AC than KFMB 100.7, using the slogan "Superstars of the 80s and 90s."
Sorry I don't have more confirmable dates, but that's how I rememeber it.