A good question, and one that even good coaches rarely agree with each other. Here is some general info regarding squats and leg presses.
a. Absolutely start at a weight that your whole body can handle.
b. Work up gradually such that you ensure not hurting the back or any other part of the body.
c. Keep moving up as long as the whole body can handle the weight, doing high reps (30 or more), about 3 sets.
d. Given that you don't damage your body, there is no such thing as getting too strong, given that we're talking high reps, and multiple sets.
e. Continue getting stronger until the season will not let you lift anymore. Some good cyclists will continue lifting on Tuesday mornings, just to hold onto the strength as far into the season as possible. One thing you will learn is that no matter how hard you train and how many miles you ride, there is no way you'll be as strong at the end of October as you were when you started racing in March. So, weight lift as far into the season as is practicable.
Whether you're talking sprinting, uphill sprinting, or climbing. the stronger you are, the better. However, during weight lifting season, make sure that you are also riding the bike and doing other bike specific training that also builds pedaling specific muscles.
When I was in the Marine Corps, I went in able to about 50-60 pushups. After doing 10,000 a day for about 5 weeks I could pump 100 without even slowing down. It's no different on the bike. If you are very strong, that is very good, because you can call on all the muscle and sprint the hill better than anyone, or you can use a small part of it and have your leg muscles coasting while they are sucking up all the oxygen your lungs can produce. These are my thoughts. Stronger is better!