I got the sequence of events a bit confused, but after going back and thinking things through, I think you guys are right and this is the correct sequence of events (assuming the memories Baku gave Yuukide were 100% accurate, which is unlikely, but fairly possible. At least the big events will probably be accurate):
??? 1998: Baku and Hachina meet at the bookstore (in my opinion, probably for the first time). Hachina becomes Hal.
November 23rd, 1998: Baku plays Pooyan, Hal is at his place when he comes back, throws his Pooyan run (what a sin). Afterwards, Baku apparently falls asleep or gets drugged, and Hal goes to Baku's big gamble of that day in his stead. Hal dies/loses his memories/gets sacrificed. (I wonder how accurate the other things are, too. Like him eating Eel with pickled plums the day before, and not getting enough sleep. I guess we'll see).
Baku probably continues being active as a Kakerou member. Eba dies in between here too, probably.
April 9th, 2001: Baku takes on the StL game with Kakerou's Leader, who, to his surprise, turns out to be his old friend Hal, who he thought died/was gone, and probably doesn't remember him anymore. Thus, Baku decides to throw the game (probably).
After losing, assuming he didn't become aware of Souichi's survival in the time between Hal's "death" and the StL game, he at some point buys Eba's friend's bookstore, in the hopes that one day Souichi will lose his memory again, do the book ordering trick again, intercept it, and meet him, hopefully as Hachina.
Mainly speculation, but I think the main events should be accurate enough. We're finally starting to get a glimpse of Baku's backstory and his true motivations. Curious to see how far Baku and Hal's friendship will go, and the details of the gamble where Hal "dies".