Hardly a pain. I took a quick course at the local library which showed me how to use iMove HD (06), or I would never have had the confidence to even try to make video.
I am no pro, just a home user, so here are my thoughts on iMovie vs. fcpx
1) FCPX will work well with the panasonic you are considering.
2) FCPX, for all its quality, isn't that difficult an application to use. But one really needs to take some tutorials in it first. There are a lot for free online, and others that cost a few bucks that are great. Some suggestions include Izzy Video (free), Ripple Training (low cost) which is downloadable, Tom Wolsky's tutorials, and a lot of others on Youtube and elsewhere.
3) There is no absolute need to purchase fcpx. It depends on your needs. I used iMovie for years and found it to be great for youtube video. Yes, the quality upon export isn't as good as final cut, but then it comes free with every Mac, and for a small window Youtube video, it is actually very good. And if one spends time with the latest iMovie, then one can move to fcpx easier, as fcpx works a lot like iMovie.
4) I found iMovie difficult to learn, so that tells you something about me. I have no doubt, depending on what computer you use and your interests, that if you can master iMovie then you can use fcpx. But I am not kidding when I say that going through some tutorials is essential. Previously I have bought both Ripple Training and Tom Wolsky's tutorial and found them darn good. And Izzy has a real talent for explaning complicated stuff simply.
5) Exterior mics. I use a small Sony mic, that I bought when I got a sony camera. But it is expensive at $149, and there are nice alternatives, like this one from Rhode. I like the Sony, even though it has a hotshoe that only works with Sony, because it it small, and I can velcro it to any camera I have. I also bought a Zoom H1, and have used that connected to a lavalier mic to get good sound from a speaker.
Hugh