Stretch after, not before...shouldn't stretch cold muscles, warm them up by taking it easy for a few miles
Calves, quads, glutes, hamstrings I would try - plenty of info on the interweb
100% on the money
--From my notes--
A gentle warmup aids the secretion of synovial fluid. This fluid if you will is like butter in the microwave. Hard until you heat it, at which point it becomes a lubricant for your joints. Going straight into a stretch is going to overwork a muscle that is cold,against a joint that has little to no protective lubricant. I'm sure you can see where that is heading.
The aims of most warm-ups are to increase your HR gradually - increase blood flow to working muscle - and really just prepare mentally.
You can warm-up passively - This is basically having a hot bath or putting on extra clothing. This doesn't target muscle groups to be used,and it wastes the hot water you'll need later
Or
Actively warm-up - This is a warmup which involves similar movement patterns to those of the muscle groups to be used. That could be barbell curling with an empty or very light bar or spinning a low gear on a bike - with a gradual increase of intensity and HR or weight respectively.
The aim of a post ride cool-down is to return the body to the pre-exercise state. IE: as it was before you left the house/work/garage/ wherever.
Enhances venous return (allow blood diverted to working muscle to return gradually and help prevent pooling which can cause dizziness and nausea - in extreme cases CVD) If you've got off your bike before and felt a bit woozy, chances are ^ it was this. Triathlete brick sessions is a good example of combatting the effect. A fast 40k into a 10k run isn't fun when your legs don't want to comply.
And again psychologically - feeling ready to go at it again is much better than feeling that your planned ride will be crap due to fatigue :P
