Your plan (1 night Horse Camp/1 night Lake Helen) sounds like a good, conservative way to do the climb.
Many will disagree, but I am convinced that rushing up from sea level and sleeping at 10,400+ is not a good way to acclimatize. I would put the priority on getting a good night's rest. The day sortie should help reset your respiration rate to the higher elevation.
Night 2 at Lake Helen has the disadvantage of the weather/wind issue (I've been hammered by wind up there), plus the additional elev. which could make sleep difficult.
That said, it's a long way from Horse Camp to the summit. Cutting it in half is probably a good compromise.
You might enjoy the Avalanche Gulch Trip Report I just posted on my site.
Andy
