420's, 450's, (etc) windless' are wired the same as you describe... ie, dedicated panel breaker for windless which switches large D/C breaker next to panel supplying DC power to windless via large gauge wire run up to the bow.
After discussing powering washing down pump w/ service guys at Norton Yacht Sales, I took power off from the windless lugs (up forward), routing wiring to the washdown pump thru an on/off switch (located on the wall of the fwd head). This saved snaking wiring from panel forward to washdown pump.
But, adding another dedicated panel breaker for washdown pump as you describe, may be a "more correct" way of wiring the it... not sure.
I am sure that I've has no problems with the way my washdown/windless has been wired for the past 12 years.