A freelance TV & TVC director based in Sydney Australia.
Mainly all musicals are normally shot and lip synced to on set playback (the latest Les Mis being a really good example of why using on set sound isn't a great idea). But my advice would be to get as many cameras as you can (I would say at least three if you can). That's the easiest way to make sure you can capture the performances and let it cut properly if you're doing something that need proper continuity. You'll find that multiple takes for the same sections will quickly erode the freshness and tire your actors. Also rehearsals are key and incorporate your camera moves in them so it's really just a matter of turning up on set and doing what you've been doing!
Hey David, I have an A7s which I bought to muck around with (I normally direct rather than shoot). It gives amazing low light images and the video quality is amazing. Just a warning though, the rolling shutter is absolutely terrible in full frame mode, so if you were going to be mobile with it, even panning back and forth slowly manages to make it show up. Also the battery life is pretty poor but you can rig it up with an external. Im using it primarily as a stills camera at the moment so I went and grabbed the battery grip which lets you run 2 batteries which is a life saver. Also if you're shooting log on the A7s you have to shoot at 3200 ISO which means you'll need some NDs to be able to go out during the bright daytime. Plus to make it shoot worth for a doco, you're going to be spending more than 3k (to get XLR ins its another 900 just for the Sony adaptor). I would almost suggest trying to find a second hand Sony FS100 for that price. It will do 60FPS @ 1080p with a proper video form factor...
I agree with everything everyone has already said, but would just like to add always treat your crew right and with respect. There are a lot of directors out there who think yelling and screaming and tantrums are the way to motivate people, but I find when stuff inevitably goes wrong, a crew who are willing to go the extra mile for you because you're not an arsehole can really save the day!
I'm a director / editor based in Sydney, Australia. I finally got around to making a reel (first one in 4 years) https://vimeo.com/104807095 its a combined directing/editing reel (70% directing/100% editing) of stuff I've worked on over the years. For more info on the individual projects you can check out my site: www.fireallweapons.com Thanks!