The important bit to get sturdy sprouts is to get the light/heat balance right.
Is piglet suggesting not putting them in the window - that's a mistake I think.
If they do grow too rapidly you can slow them down by bunging them (carefully) in the salad compartment of the fridge this will effectively stop growth
On height, a couple of inches is ideal, but if they are longer, don't worry, you'll just have to be carefull they don't break off as you are planting them. Trials have been done with sprouts up to 12" long and they were quite satisfactory