I like to stretch at the end of my workout. Sometimes I'll do it between sets, but it's not a regular practice. You should read about different types of stretching. Dynamic stretching is good before a workout, but you want to hold off on static stretches (typical stretches) until your muscles/tendons are warmed up.
I eat before and after working out. If you are trying to add some bulk eating after you workout is very important. Post workout meal should be very high in protein with a lot of carbs in it to replenish your muscles. Pre workout is mainly about fuel so you want to concentrate on carbs and fats. Everyone has a different preference for what they eat before they workout. Mine are sweet potatoes, almonds, and blueberry bagels.
Biking is really effective, but it's also pretty easy to get good at it. I used to bike now and then and would do 20 miles on trails without even being in that good of shape. If you are doing a lot of hills or anything that is very intense it is great exercise. More important than the actual effectiveness of the exercise is the enjoyment you get out of it. Consistency is key so you need to be able to enjoy yourself.