How can I keep my guitar in good health? Like temperature and humidity.
The rule of thumb is that if you're comfortable, your guitar probably is too. So not too hot, not too cold,and about 40-50% humidity. If your home has a modern HVAC system you're probably fine - if not, there are humidifiers and dehumidifiers that you can put in your case to keep the humidity in range.
Can a very strong capo damage my guitar?
Damage it? No. But a very strong capo can cause your frets to wear a little faster. If it's so strong that you're worried about it, get a capo with less spring tension. I think Seymour Duncan just came out with an entire line of reduced tension spring capos.
How can I prevent bridge damage?
On an acoustic guitar the bridge is glued to the top, sometimes with additional pins that go through the top to the bridge pin block. Other than keeping the temperature and humidity right, you can't prevent glue joint failure, but you can check for it - if you can slip a business card under the bottom of the bridge, take it to a luthier. The earlier you can catch a glue joint problem, the easier it is to fix.
Is it normal for other bridge pins to be elevated a bit?
It depends on the bridge and the pins. Most don't seat all the way down, because you want the bridge pin taper to provide friction to hold it in the bridge pin block. If one is higher than the others, you probably have the ball end of the string seated incorrectly. Loosen the string tension (a lot - you want it really loose), pull the bridge pin, make sure there's plenty of string in the hole, reseat the bridge pin, pull the string up while holding the bridge pin down, and tune back to tension. If you see the bridge pin rising up again you might need a new pin - they're cheap.
Why is my guitar's strings buzzing?
There are too many possible causes to diagnose from that description. But since you're a beginner, the most likely cause is finger placement - the farther away you are from the fret, the more likely you are to get a string buzz. Your fingertips should be as close as possible to the fret without being right on top of it.