After many years of living with someone who had their own spray shop I would reccommend going for celly. Synthetic sets like rock and is harder to rub down if you make mistakes, so I've been told. Just keep each coat nice and light. I presume you will use a one coat, not a base coat and lacquer (spelling).
Just one thing to remember, if your vehicle was originaly painted in celulose and you decide to go for synthetic, there could be a reaction between the two paints and either cause bubbling or a rather nice effect similar to the "crackle" finnish you can do on woodwork, but I think you can get a primer to stop this.
If in doubt pop the vehicle along to your local paint factors and ask their advice.
I've masked up and preped many a vehicle for spraying in the past, so if you need any advice on that side of things I'll be glad to help