I am guessing you are in a slip with one of the condo's along Rainer or Renton Ave that traverses the south side of the lake from Seattle to Renton? Should stay pretty calm there over all no matter the weather and wind.
Go ahead and winterize, if you come up for a sail, then unwnterize the motor, leave teh water out of the water tank etc, and you will/should be fine. Some winters it is rarely below freezing around here, others......well, not fun for this area.
As also mentioned, there are lots of places to see and sail around here. I also am recalling a YC near you, Rainer beach YC. Also to the north a bit on LW is Maydenbauer bay, and newport YC just south of I90. If you are looking for close by YC's to join etc.
LW s a fun lake to learn to sail or just plain sail on. I grew up tween Kirkland and Juanita bay sailing north of 520 as a teen. Every once in awhile, the wind would kick up, and my step dad and I would sail from Kirkland around MI and back home. Did that once with winds in the 15-25 range, what a sail back to Kirkland!
Enjoy your time here.
She drives me boat,
I drives me dinghy!