In the dialogue quoted, Riker asks of the Stargazer's former condition "What was Stargazer's condition" rather than what is it's current condition. I take Data's reply as the ship's status when it was abandoned.
This could just as well refer to the analysis of the ship Data personally did some time ago. Indeed, that would be the logical question to ask, because Riker has no interest in the past condition of the ship at all - the only thing relevant is her current condition. Which Data established in the recent past.
It's no different from Tasha asking "You transferred some of his belongings?" in imperfect when wanting to know about the current status of Picard's luggage.
OTOH, how many shuttles could the Stargazer hold and would it be enough to carry all the crew?
If the ship packed the shuttles like we saw in "Mudd's Passion", even the bays envisioned by Sternbach in the cutout drawings would hold the necessary twenty or so easily enough. But that is probably not an operational setup, but more like a temporary "Cleaning the Lower Hangars Day" reorganizing of the onboard fleet.
Then again, Picard's "we limped
through space in shuttlecraft for weeks" might refer to the shuttles towing warp-incapable survival aids, as "limping" IMHO is not something an undamaged shuttle would be doing by default. Quite possibly the ship deployed a range of "propulsively challenged" shelters that added to the total evacuation capacity.
Regarding putting out fires by taking away the oxygen, this probably doesn't work very well on starships. We have seen flaming wrecks often enough, after all. There are probably alternate sources of oxidation aboard; perhaps standard interior materials keep on burning on their own once sufficiently heated, and Starfleet accepts this because if the interior is that hot, everything is lost anyway? (Cf. use of aluminum for ship superstructures and APC armor today.)