what time would you guys say is best to arrive in front of the castle and get a good viewing for the fireworks at 10?
This all depends on the time of year and day of week you go. I have been and got a good seat with only 30 minutes to go, others I have sat for 1.5 hours. The best bet is to go there an hour before the show and get a feeling as to how busy it looks.
Fireworks you can see from quite a distance away, Dreams you need to be nearer.
As Grovesie said, it all depends on how busy it is and also what the weather is like. Last August we got to the front about an hour and a half before (take something to keep you occupied!). As we were near the front, we could sit and wait, we also sat through Dreams too.