This is my first time growing brussels sprouts. I was told to remove the lower leaves in order to get larger sprouts. This is a common misconception. Garden catalogs often have pictures of brussels sprouts with the lower leaves removed. This shows off the sprouts and entices gardeners to buy.
Farmers often remove the lower leaves to speed up harvesting.
I recommend you leave the leaves intact. They produce the energy for the plant. The more energy produced, the bigger the sprouts. Sprouts are ready to harvest when they are firm and one inch in diameter. Their quality and flavor is best when the sprouts develop during cool weather.