Adam, here is an attempt to discuss the excellent questions you pose:
1. Since load and high stress seems to be what killed off wooden blades - what if I had more blades and therefore spread the load between more of them? Then they could be thinner and more agile, no?
Wood as a structural material has great limitations - it cannot be strong enough without being made very thick - ok for buildings, pretty bad for blades. Much of the stress is not because of the number of blades, it is because of the need to have them aerodynamically thin while they have to be skyscraper-strong. The combination makes wooden blades a marginal idea.
2. Isn't there a benefit in having more blades in that since they can share load, they can also create more lift per revolution. It must be easier to create X sq.ft of lifting area spread over 8 blades rather than over 2. And 8 thin-ish blades must make less noise than 2 huge ones.
Two issues here - the real issue is the amount of blade area for the weight of the helo. More thinner blades are in the same hole as fewer thicker ones. If you made the greater number of blades wider in chord and thicker, the wood would work, but the blades would need much more engine power to swing them around and make the necessary lift. More power than the skinnier metal or composite blades.
3. A big rotor diameter means that the rotor can turn slower (since the tip speed limits the design of any rotor). Slow turning rotors create much less noise. Why isn't this done more on helicopters?
Very true, but slower rotors stall earlier, and have a lower Vne, and lower cruise speed. In fact, that is why older helos have Vne's at about 100 knots - they have slower rotors and less blade area. Good for noise, and hover efficiency, bad for high speed.
4. The constant chord design of blades seems easier to construct, as you guys pointed out. But surely, the twisting if them to create wash out must be a rather finicky thing to do. It must be very hard for two twisted blades to have the same twist at exactly the same point throughout the blade. This must create a vibrant and unruly rotor path that needs a lot of tracking. So my question is still - doesn't a variable chord rotor (that doesn't need to be twisted and matched up), create less of a headache in the end when all the work spent tracking the CC one has been factored in?
Lots of issues raised here: Twisting a blade isn't hard, and making two or 1,000 of them exactly alike also isn't that hard, really. Variable chord could work, but the chord would be screwy - thinner at the root, thicker in the middle, and then thin at the tips. It would be harder to make, but not terribly, but the aerodynamic advantage would be slight, I think.