I have a 2001 EC200, but mine has the motocross ignition (lighter flywheel, more zap, less wattage for lights though) so it's like the DE bikes.
I think the bike would be pretty much perfect for your son. The bikes make really good power that's pretty smooth. Though if it's a DE, it will definitely have a hit in the midrange. Handling is second to none. As far as suspension goes, the stock stuff is decent, but to get the most out of the WP fork, get it revalved. Pro Works Racing did my suspension and I'm really, really happy with it now. I ride everything from sandy whoops to roots and rocks to mine rock and even a little motocross and have found that the revalve has given me a ton of confidence. The suspension soaks everything up.
For jetting, my bike was bought used and the previous owner had already dialed in the jetting. I had heard some issues with jetting the bikes though. Talk to Les at LTR for any help. His jet kit is supposed to do wonders, but I haven't tried it yet.
As far as reliability goes, I have 3 hard seasons of racing and riding on my top end and compression is still great. The bikes are very durable and hold up well under tough riding/racing conditions. The only problems I have had are a broken needle holder in the carb (completely out of the ordinary, easy fix though as KX250s use the same carb) and a broken rear brake pedal (my fault, I hit a stump). Besides that, the bike is bulletproof.
For dealers, most GasGas dealers are really good. The absolutely best one I've found is GoFasters. These guys are awesome. Check
www.gasgasrider.org for all your GasGas questions.
Oh, and if the bike is bone stock, here's what I recommend adding:
-Skid plate, pipe guard, barkbusters
Performance wise, I've heard good things about the LTR powervalve cover, but I haven't tried it yet. I should be getting one soon though so I'll let you know how it works out.
If you need any more info, just shoot me an email or post here.