1. I'd rule out the Kobo. Cheap but flimsy.
2. Then I'd go for a 505. You only get them used these days but they are build like tanks.
3. It is a great gift for everyone who loves to read and if he is responsible he will not loose it.
4. There is no need for money.
The Singapore Library is for free and has a selection of nearly 3,500 childrens books. Even if only part of this might be suitable for his age it should keep him busy for a couple of years.