My car is misfiring. What could be causing this?

I would focus on #5, check compression, and based on result you may be also looking at a leakdown test. It could be faulty injector, or mechanical problem such as a broken valve spring, or valve itself. Does it misfire under load, or at all times. Under load usually suggests secondary ignition, all the time could be fuel or mechanical. Idle-only misfire could be result of excessive internal leaking(valve face/seat). A leakdown test can confirm this.