After all of my thinking, reading, debating, and posting . . . I decided the best place to start the A-series is A1, Part A.
So that's the plan. The PCs will go through both parts of Slave Pits of the Undercity, using the nine pregens. It remains to be seen if they'll go for pure tournament (meaning, the PCs are reset to the tournament status for each module) or "continuing play" - they can keep and use the loot they find but don't gain automatic upgrades and equipment replacements.
I'm leaning to the former, but we'll see after we get started.
A1, time to make rosters and cheat sheets.