Yes you can double up on wetsuits, but like mentioned it opens a whole new can of worms, mainly it cuts down on your flexability. The best way to double up wetsuits is to go with a full suit and then a shorty over it (Short legs and short arms), this keeps your core warm but allows movement. It's still not the best option though. Like already mentioned the best set up is a good 3/2 taped and sealed wet suit for regular riding and then, for when it starts to turn cold, use your taped 3/2 along with a tour coat. The tour coat does the same thing as a double up wetsuit but its way more flexible. If its too cold for the taped 3/2 suit and tour coat combo then you need to get a good dry suit. Thick wetsuits aren't the answer because they cut down your flexability. For your extremeities, for your hands use your regular riding gloves and hand warmers. Thick wetsuit gloves will give you major arm pump. Properly set up handwarmers keep your entire hands warm. If your handwarners aren't keeping your entire hand warm, then your set up is probably wrong. I see shot-ty, worthless, hand warmer set ups all the time. Since your feet don't really need to be flexible you can go with thick rubber like a scuba or kayaking setup. When it comes to feet, I prefer to rely on thick enough rubber to keep my feet warm instead of some sort of hand warmer set up because your feet do go in the water much more than your hands so they should not be relying on a running engine for warmth, plus having both foot and hand warmers robs your hands of needed warmth, and if your hands are cold, your whole body is cold.