2.8 still sucks for shooting indoors on the GH1 (when you don't have control over the lighting), IMHO. And outdoors, yeah, you're going to need something like a FaderND if you're stuck in f2.8. Even on the kit lens, when shooting outdoors, you gotta stop it all the way down (I don't use my FaderND at weddings...I don't care about super shallow DOF...and it's a PITA to take on and off every time I go outside). If you tried to shoot f2.8 in the Sun by just speeding up the shutter speed, it would be interesting to say the least. I know a lot of wedding videographers do it...I've seen their footage.
And at a focal length of 28-75, you lose the best of both worlds. It will still be a "telephoto" at its widest end (56mm equiv), and still way too short at it's long end to shoot church weddings. Unless, of course, you have a shooter like bronxjragon who runs point blank around the altar area with a camera mounted on top of a long pole.
j/k (I know that "unobtrusive" is not in the vocabulary of some cultures, and if you don't shoot the ceremony point blank, you'll be blocked by 4 photographers and 10 amateurs with photo/video cameras standing around the altar. lol It's just not my style...and would get me kicked out of most churches.) Ideally I need at least 200mm/f2.8 (or better) for ceremony shots.I wouldn't bother with a directional mic plugged into the GH1. The 2.5mm jack/plus adapter was a major point of failure for me, and there's not much to gain, since camera mic is usually crap audio anyways. The built-in mic is good enough as is, for ambient/sync track stuff. Spend the money on digital recorders instead, to get mics closer to the subject/musician/speak cabinet you're trying to record.
I shot a 4-hour wedding/reception, plus 60 minutes of pre-ceremony, EASILY on two batteries this past Sunday. The previous week I shot a 9-hour wedding/reception with 4 batteries....all with the LCD open.
I'd probably stick with the Extreme III cards. I use Ultra II in my GH1 all the time, but when shooting home video with the GH13 I use Extreme III (I won't use GH13 for weddings). I'd probably feel safer using the Extreme's in a GH2 if I upgrade as well. I've used a lot of Transcend cards for audio and video recording. I wouldn't trust them to video recording again. I'll stick with Sandisk for video.
Good luck!