The FX300 kit will include a throwout bearing, NTN brand I believe was in mine. I succumbed to fear-based marketing and went with the TSK3 kit though. You should also replace the pilot bearing while you're in there, and I don't remember that coming with the clutch kit. I went with the 06+ WRX fitment SMFW which came with a new pilot bearing in it already. Since you need to get the flywheel resurfaced, you might as well source your new pilot bearing ahead of time, that way you can have the machine shop press that in for you.
In theory, your ACT flywheel should work, provided the flywheel and clutch kit are both supposed to fit the same year & model of car. Whether it will work in reality, I guess you'll find out. Not sure what clutch you're running with it now, but the FX300 is slightly "grabby" on engagament. For the daily driving in stop-and-go traffic that my car sees I probably wouldn't choose to run it with a super light flywheel, but that's personal preference.