Accent MC (2006-11) :: Low Purge Flow And Misfire - Transmission Shaky At Higher Revs

I have a 2009 Hyundai Accent 4-door 1.4L auto, 123,000 miles.

Before you ask: The high mileage is because it's used for a newspaper route. We(as in, myself and my father) take great efforts to keep it in as good a shape as possible given the amount of stress this puts on it - one minor deer impact aside, I think we've done a good job.

Recently(read: a week ago), we replaced the purge flow valve due to it causing stalls and difficulty starting after refueling. After a week of apparently fine operation, as I was nearing completion of the route, a very clear cylinder misfire began. Not the worst misfire I've ever heard - the car barely seemed to struggle on initial acceleration(except in reverse, which made me slightly concerned I wasn't feeling an engine issue, but a transmission issue), and only got really shaky at higher revs.

We have an OBD-II reader at home, so when I returned I plugged it and discovered not one, but TWO error codes: P0497 -low purge flow- and P0301 -Cylinder 1 misfire- with the reader listing them in that order.

Looking up information on these two being connected has turned up little support - I've only learned that either one can be cause and effect. Needless to say given timing I strongly believe that it is highly likely that we either made a mistake installing the new valve, or that the new valve was bad from the get-go.

We'll be checking the spark plugs as soon as we are able(I am about to go to sleep and my dad has work - we tag team automotive repairs since two sets of eyes and two brains can figure things out better and an extra set of hands is always good to have ready even if only one set can actually do the job), but even if the problem isn't the spark plugs, it doesn't automatically mean it's the purge valve, either - at least as I understand things.

So with the background out of the way, my questions are thus:

1) Is the spark plugs don't fix anything, what is the quickest way to figure out which error is cause and which error is effect?

2) Are there any serious risks to continuing to run the car in this state if a fix cannot be made immediately? (being able to borrow another car is possible, but problematic - need to stick with this car if safely doable)