Have you considered how your going to vent the fan? You need to find a way to get it outside the house. You should not blow it into your attic or soffits. You may need to remove more drywall than you think. The drywall should hold fine unsupported by the wall sheets however if you are going to install new drywall, why not remove the old drywall first? You will have access to deal properly with your fan/light and ventilation. It is not that much more work and unless there was something like loose insulation up there. Even then it might be worth dealing with. One layer of drywall is lighter and easier to deal with when it comes to things like recessed lights and ceiling fans. Some times the clips that hold the housing in place need that 1/2" above pane to be wood and create the plane by attaching to the joists or strapping (depending on your location) If you are going the patch and skim rout and you have not done it before, it could be time consuming and difficult to get the results you would want. Good luck with your project!

you could go with 4" also for the 9' ceilings, but either way is good.

Hello, I'm trying to replace the burned out bulb in the pictured lighting fixture - can't tell how it's attached (doesn't seem to screw off, and I tried the push and twist method as well), so wanted to see if any of you had some insight into the solution. Have taken on (another bulb) and off pictures of the installation, thanks in advance for the help!

Can you post a photo of the trim? Some trims are really standard- they can be replaced for $10-$18 at home depot plus $5-8 for a good bulb. Sometimes they are not standard but can be fixed with a can of white spray paint. Then other cans have trims that are integrated and can't be removed at all... Generally working with what you have will be cheapest as it doesn't require an electrician to replace the housing in the ceiling. To me LED bulbs have a better light output than the LED retrofit kits, others will disagree. Make sure to watch the color temperature (I like 2700K) and you will need to replace the dimmers as well.