Just go for it! If you can confidently tune a 2 stroke, then give a thumper a try. I've had OS and YS and tinkered with friend's Saitos and believe what people say in terms of reliability. The Saito and OS are 1,2 respectivley. The YS engines provide incredible power, but at the tradeoff of finicky tuning. Once you get one dialed though...they are knida bad to the bone! OS has a really cool vavle adjustment tool kit that works on most engines and is worth every penny. As long as you don't try and run too much nitro or get them too hot, you'll find nothing more that a quick check of clearance is all that is required for the valve train.

One other thing that I don't think I read was the fact that a 4 stroke is much easier to make scale or custom exhaust systems for since they don't require an expansion chamber like a 2 stroke.