Sennheiser G3 is solid- used on plenty of pro productions, which the Sony isn't. Get yourself some manicuring scissors and moleskin, and do a little research to learn how to best mount the lav- that will make a bigger impact on your sound than the choice of brand. Wouldn't recommend having subjects hold a mic. If you don't have time to place a lav, just get your Rode on-cam mic as close as possible (keeping in mind the pickup pattern of the mic) and try to find the quietest place nearby. You'll probably need a sound-isolating shock mount for your Rode or you'll hear camera handling noise and possibly lens noise. And you'll need wind protection for it if you'll be shooting outside- get something like this that fits your mic. Turn off auto gain control on your cam and set levels manually.
D-word can help with tech stuff, but is better suited for creative issues. You'll find more detailed tech advice at a place like dvinfo or dvxuser. Good luck, and come back and post some of your work when you're ready!