Well my first experiment was a disaster (too many new/unknown factors)
but the second was very promising. Kenneth, it looks like you were
right about the dryness of my original dough. Thanks again to all for
the great advice.

I've got one follow-up question: how does the starter itself figure in
to the hydration measurements? I'm using 400g of flour, so that's 300g
or so of water -- does the starter count as part of the weight of the
water, or do I make an estimate of how to split it between flour and
water weights? Do the quantity and liquidity of the starter make much
difference to how the dough behaves?

Thanks once more, this has been tremendously helpful! And I'm now
keeping a bread journal.

Yours,
Eric