base layers

I don't think it's a bad idea per se, but it seems like you wouldn't be getting much out of that second "baselayer". You might as well carry slightly more weight in a "mid-layer."

A L/S Cap 1 Silkweight lists at 6.1 ounces (I'm assuming this is what you are wearing). So, a Cap 3 Zip Neck L/S lists at 7.8 oz, only 1.7 ounces heavier. A Cap 4 Hoody lists at 8.5 oz, only 2.4 ounces heavier (with a hood). The Ibex Indie Hoody lists at 8.8 oz on their site. I think you'll get a lot more out of those tops (or something similar from another brand).

You can then wear any one of the shirts to sleep in and shouldn't be overly hot at those temps, even in the hoody.

yes. A LS cap 1 silkweight top/bottom. The heavier set would be smartwool merino midweights top/bottom. True..its only a difference of an ounce or so..

If it were me, I would bring the heavier base layer just in order to have something dry to change into at night in case I mistakenly sweated.

del

I agree on the Cap4 Hoody. I still have and occasionally use an Indie Hoody, but like the Cap4 better.