I might have opted for 25mm gatorskins, but 23's should be fine.
I am not a fan of backpacks for bicycling. Maybe a handlebar bag or seat bag if you want to carry more than will fit in jersey pockets.
Be sure you are prepared to fix a flat and do minimal repairs or adjustments. A tiny seat wedge is probably enough to carry stuff for that.
What is the route like? Depending on that maybe some lower gears if in the mountains much.