Maybe an Amiga 500 might be a bit too complex for a 5-year-old at start. It would be great if you had a Commodore 64 for start. Then give him the Amiga 500 when he turns 8 years old. :-D Best thing to write disks is getting them from
http://www.back2roots.org . You will need an Amiga to write the disks back orginally. You might be able to talk to someone who can probably sell you original copies of games if they got any if you cant write the ADFs.