You are wonderful to do this! Down the road, you'll be so glad you did. If you can keep him healthy so he survives to adulthood, your RES will be your friend for life. You will never be sorry.
On your specific quesitons:
1. For a 10 gallon tank, you need to change it at least once a week unless your filter is doing a super job. Perhaps more often. Smaller tanks require more frequent water changes than large ones. And the more water you put in the tank the longer you can streach the time between changes. For sure change it when the water starts looking crudy or starts smelling bad. When you change the water, just gently lift your little turtle out (keep a firm grip - they are unbelievably squirmy) and put him in a plastic tub or bucket. I like to put a soft towel or wash cloth in the tub so if your turtle falls over he'll have something soft to land on. You can put another towel over the top so it's dark and he may take a nap while you change the tank. To get the water out, use a syphon. Do you know what a syphon is? You can get them at the pet store or you can make one out of a plastic tube or a piece of flexible garden hose. Syphon the water into a bucket. Then clean and clean the inside of the tank, and refill. Make sure the water isn't ice cold or too warm.
2. Yes... remove the pebbles. It will not only make cleaning a lot easier but they are very dangerous if your turtle eats them. Your turtle will appreciate having something in the tank to play with. Since he's really tiny, you can put a coffee cup in there and he'll hide in it. He will also need something like a plastic plant that reaches up to the top of the water. They like to hide in plastic plants and they rest on them near the surface when they get tired swimming.
3. You'll need two light bulbs. One can be a regular household incandescent bulb. It's for heat. The other will be a fluorescent UVB bulb. Turtles need UVB to process calcium for their bones and shell. The Reptisun 5.0 or 10.0 UVB tube fluorescent are good bulbs if you have a tube light fixture. If you want to use a regular light fixture you can get a Reptisun 5.0 compact fluorescent bulb. It's good but don't get the Reptisun 10.0 compact fluorescent bulb as it's too strong. Here's a photo of a really nice setup with two lights:
http://www.redearslider.com/forum/viewtopic.php?t=8890
Leave the lights on for 10 to 12 hours per day. You can get an inexpensive timer (around $5) at Lowes or Home Depot that will make this automatic.
4. Here's some good brands of pellets and how much/often to feed. Repti-cal is on the list:
http://www.redearslider.com/pellets.html
5. Down the road you'll need to be concerned about these things but for you if you change the water frequently you'll be fine.
One thing you didn't ask about it temperature. This is important to keep your turtle healthy. You need to maintain a water temp of around 78 degrees while your turtle is little. You can get an inexpensive submersible water heater at Walmarts. Someone on here calls it the best preventive medicine there is! You'll also need a thermometer to measure the temperature of the water and the basking area. Again, you can get very inexpensive thermometers for this purpose.
That should get you started! Come back as you go down the road and have more quesitons!
Again - good for you for taking the little RES!