It's wonderful that you've been able to improve Shelly's living conditions. Hope you don't mind a couple of pointers/questions to help you.
Gravel shouldn't be in an aquarium for turtles. Turtles will eat anything smaller than their head and this can lead to impaction and surgery, which isn't good for a turtle. Many keepers find out that their regular tank cleanings are much easier without anything in the bottom, or large river rocks.
The lights that you said you have, is it both lights needed especially for turtles, a UVB bulb(simulates sunlight) and a UVA bulb (heat). It is extremely important for turtles to have both of these.
When measuring a turtle you measure SCL (straight carapace length). Measure his shell from tip to tip not including the curve. This is how long he is. If he' s more than four inches you can tell what sex he is. Male turtles will be physically small growing to be 7-9inches tops. A male will have EXTREMELY long front claws (think Edward Scissorhands) and a thicker tail with the cloaca closer to the tip of the tail. Females are physically larger growing to be 10-12inches in length. They will have small front claws, and a smaller tail with the cloaca closer to the shell.
General rule is 10 gallons of tank per inch of shell with as much water as you can fill it without them escaping. Be sure he has a basking dock that is under the lights and he can completely haul out of the water and dry all parts of his shell.
Keep us posted about how he likes his new tank and if you have pics we'd love to see him.