Having made a few now for experimentation, I've got a few things sorted out. The 'pattern' I had been following called for 14 chain - 15 beads with chain in between (29) - 14 chain. The length is perfect, but I'm happier with the ballance at 11 chain - 18 beads with chain in between (35) - 11 chain.
I'm also happier with the finishing bead near the clasp. Not too large to give your fingers difficulty putting it on and taking it off, but substantial enough just to finish it off.
I tried the large seed beads for the start and ending chains again, but this time with colours that would be more visible, and continue the design around. You could certainly use just one colour, or all sorts of colours, but in this case I kept it simple with two colours, doing a strand of each.
The third strand I did just with the wire, and I'm happy with this choice as I did a little test, and I think that three might be too much.
For this blue and silver necklace, I continued the large seed beads in the "in between" chains where the beads are - on two of the three strands. I think it adds to the design, and probably even more so when not using quite so many large beeds.
We're getting there!