Botto and umd (and others, who have some experience on their side) not withstanding, I think less is best. Here in Los Angeles – and Southern California – in temperate conditions, I wear a jersey and cycling shorts, cycling shoes and socks, gloves and a helmet. That's it.
Yes, I have a base layer. However, I only wear it when it's cold (by S. CA standards). For example, I wore my base layer last weekend in NYC, where the temperatures ranged from 30 degrees F up to the low 40s, with some serious winds blasting out of the north. (At that point, I also wore leg and arm warmers, tights and a windbreaker, and a winter cycling cap.)
umd wrote: "They are all very tight against the skin and made of materials designed to wick sweat away."
My jerseys are reasonably snug and designed to wick sweat away. For me, a base layer is duplicative if it's not cold.
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