It's funny, DS9 really is the only series where we have no real clue about how many crewmen or visitors are on board.
We know it's operated by Starfleet and Bajor in cooperation, with Starfleet (Sisko) being in the lead and Bajor (Kira) as 'first officer' having a big voice. Security (Odo) is mostly in Bajor's hand, with support by a few Starfleet experts. Science (Dax) and medical (Bashir) are both marginal portions who don't weigh much in station politics, so it's easy to see why Bajor let both be Starfleet: they have more experts on these areas to spare. Now engineering is also lead by Starfleet (O'Brian). But that is why Starfleet is here: To send trained personal to rebuild the station. Most of his men are probably Bajorans, with most of them probably not educated in engineering, but who learned it in the field during the occupation. That probably bugs Bajor the most, and the long-term goal may be that after the station is repaired and enough personal trained, the Bajorans can take back daily operations and engineering on the station and leave Starfleet only in some 'decision-making' positions.
But now to the rough numbers on the station:
I'm in season 2 now, and I already have the feeling that the station get's more and more crowded. It makes sense in context: During the pilot the station was trash. They even bribed Quark to stay on the station and bring life to it.
As it's a station, it probably has a very variable amount of people who have to be on board, depending on the number of visitors and technical systems that are currently active. And the ability to house a huge amount of people in general (vistors, merchants etc.). Since there are only a few big technical devices (like Runabouts and energy reactors), most of the space is probably cargo and living areas (unlike our starships, where most of the space is filled with big technical devices, like engines, reactors and shuttle bays).
In 'Captive pursuit' I had the feeling that O'Brian meant there are a total of 300 people an board, visitors included. Which in my eyes would make sense: maybe 20 - 30 Starfleet personal for the station, plus another 10 - 20 to maintain the Runabouts and docking areas, with another 100 Bajorans, most of them in the engineering corps and administration. Now, in season 2, the station is much more crowded: New shops have opened, new bars and diners (even a klingon one!), and DS9 has generally become an important hub in this sector, with ships docking and leaving on a regular basis. Therefore the number of people (visitors) could have easily been around 1000 or more, with an unsteady increase in Starfleet and Bajoran personal to manage daily operations. But I would still assume much less than 100 Starfleet officers, maybe 60 or 70, and about double as many Bajoran personal.
Now, as soon as they get the Defiant, things get complicated. I don't know if the ship has a regular crew or is made up by the station crew. But being a starship she has many complicated technical systems, like weapon systems, warp reactor and nacelles, a shuttle bay and a shuttle, all of whom require special trained personal. Since it's a small ship, let's go with more than a hundred additional Starfleet guys.
Now as I understand it, there is a big war later going on. This would mean that the station is an important base, where warships stop and get fixed. This would mean the DS9 crew would be increased heavily with engineering guys to fix the starships, but still only a small crew for station operations. Since I haven't yet seen those episodes, I'm goint to assume a few hundred guys, maybe 500, for the first time with Starfleet personal outweighing the Bajoran personal (but with a majoraty of Bajoran personal in station operations). But additional to the visitors (whose numbers may have gone down to heavily under 1000 because of the war), there is a vast amount of Starfleet personal short-term on the station, either to get re-assigned or rotating from different posts to other areas of operation. Meaning we have an additional 500 to 1000 Starfleet guys on board, who are not directly serving on the station (and out of whom 50 vulcans totally makes sense).
Now about the Defiant: Her being a warship doesn't matter at all. It would still have a cargo area, and a big shuttlebay. So even though it might be close and crowded for a crew of more than 100 on a longer mission, she would still be able to carry a giant amount of people for a short flight. When all Starfleet personal are crammed in the cargo and shuttle areas and in all the corridors, the Defiant may be able to transport way over 1000 people from one destination to the nearest base. It wouldn't be comfortable, but that's usually not what evacuations are.
In short:
So, I'm going with a very small crew for DS9 (of maybe 50 - 100 and increasing Starfleet personal with always about double the amount of Bajoran personal), who steadily increases as DS9 becomes a merchant hub, plus the Defiant crew, plus between 200 and 1000 visitors (depending on the period), and a residence for hundreds and hundreds of Starfleet guys as a military base during war.