I think i'm probably going to go with the 670 and a set of c4's.
does this sound like a solid startup system for someone that is new to this?
My opinion is that you'll get really nice sounding recordings that you'll enjoy with this rig. The C-4s are a good starter mic. Actaully someone mentioned Peluso's and those are about double the cost of a set of C-4's. What I think about gear is that there's kinda a law of diminishing returns. Yeah, a $1000 set of mics generally sounds better than what you'll be running with your C-4's but are they THAT much better. Well that's something you'll end up deciding for yourself over time. Some people are just as happy to stick with their $300 mics...others get the upgrade bug after awhile. The important thing though is that either way, you'll be pulling some nice sounding recordings with the rig you're contemplating.
16 bit vs. 24 bit. I was a skeptic at first. I've owned both the 660 and the Fr2-LE. I've personally become a 24bit believer. True, there's really no place to listen to the 24bit recordings after you get them, other than your computer, so in order to listen universally (say in your car or wherever) you end up saving the 24 bit files onto a DVD-R for the future and then dithering the 24bit recording back down to 16 bit for converting onto CDs.
Having said this though, 24bit really does sound better. There's just a more natural sound to it. It's more realisitic and more true to the performance, which is frankly what most of us are after when we go out and record. Yes, it may be awhile before we can burn 24 files onto some portable media and play it in the car, but those days are coming.
By the way, 16 vs 24 bit...those extra 8 bits are huge!!! I'm not sure I can explain this well, but the information carried in 24 bit is exponentially greater than 16 bit...not just a mere multiple. Someone explained it that if 16 bit has thousands of bits of informatin, the 24 bit has millions. I don't know if that's an accurate ratio, but you get the point. That extra detail is what makes the sound come out more realistic on 24bit recordings.
The best thing to do though is listen for yourself. Go to archive.org and download several of the same song files from a show that is uploaded in both 16 and 24 bit. See for yourself what your ears tell you. You might not hear as much a difference as I do, so it might not be as big a deal for you.
Finally, you mentioned that you'll be getting a 670. In that case, your questions about the modded 660 or the FR2-LE are moot. However, I am also in the camp that you are best to buy a stock model and have it modded by Busman. He does great mods that sound great.
Incidently, the stock boxes are great for what they're designed to do...field recording of stuff. For example, news reporters use these digital recorders alot for recording interviews and such. The problem for us music recorders is that the features of these digital recorders are fantastic, but the preamps tend not to be the best for recording live music. They're noisy, unclean and don't have the output characteristics (frequency response and such) to convey the music very nicely. So that's why you're gettting pretty much a universal response from this group that the modded units are really necessary for recording live shows.
Hope this helps!