i personally like silk or light wool baselayers. Although I would imagine one of those PI tank tops underneath your jersey will work fine as well. Don't wear cotton....or you will be drenched in sweat.
Baselayer is essentially to get the moisture away from your skin.
Insulating layer is well.. to insulate... this can be something thin like a jersey paired with arm warmers or maybe a longsleeve jersey. I was asking around about this and this year i'm going to experiment with an old thin/medium merino crewsweater. Any colder.. start layer this stuff...base+longsleeve+armwarmers and maybe throw in a vest.
I usually dont use a shell unless its a vest. If its any colder than that.. i wimp out.
Legs..i just wear shorts and knee warmers..