Seems like you’ve mostly got it figured out. Craft makes some glittens that are perfect for your temp range- the mitten foldover is a nice nearly wind proof material.
You probably only need a windshell and a slightly bigger saddlebag to fit it plus your regular spare tube & tools.
Thicker wool socks can be nice, but you may need bigger shoes to fit them. I am definitely not a fan of shoe covers as they often feel like a fifteen mile sprint’s worth of effort to put on and take off.
I haven’t come across any bibs/tights that are actually good in those temps. PI AmFibs are a treat below 45F, and are torture above 55F with any serious effort being put into the pedals.
On days where I climb in the 50-60 range and descend in the 40s I’ll often just dress for 65 and pack long thick socks, the glittens, and a windshell or thicker wool jacket (usually my Surly).