The trick to understanding weaves (I'm afraid) is getting to grips with aspect ratio (AR). This is basically the internal diameter of the ring divided by the gauge of the wire. Easiest to work in mm for this as imperial measurements end up giving you some very complicated fractions!
So if you have a 3.5mm id ring with in 1mm wire, the AR is 3.5. To get the same AR in a 1.6m wire, you'd need rings with a 5.6mm id (5.5 would work OK!)
Virtually all weave instructions will include the required AR, and from there you can work out exactly what size you need in any given gauge.
Whew!
Then there's the difference between saw and machine cut. In simple terms, saw cut will be better quality, and the kerf (width of the blade, and therefore the width of the 'gap' in the ring) is likely to be smaller.
As for coloured rings, I have to admit I rarely use them as the coated ones often lose their coating (especially near the cut), and anodised can be affected by wearing them. Same goes for plated metals sadly. However, as Alison says, you need to be careful with both, and I find the weight of the copper rings more satisfying.
Uncoated copper is a good option to learn with - more forgiving on any scratches, and much cheaper than sterling!
hth
george
