That might be a good idea if you want to copy a jacket. I think if you do that, though, you might miss the best part about custom work, getting something with patterns made specifically for you. Unless you are just bringing it in as a guideline for the kind of fit you like.
I can't say for sure. He has a very small staff so I imagine he does at least some himself. If your tailor is doing his own work I'd have even less qualms about doing a project with him. Just have a detailed conversation with him about what you want and I'm sure it will go fine. I would suggest jotting down a short note about what you want to discuss.
I would have to buy from the internet, sight unseen. Therefore consistency with sizing is of the utmost importance. If I can't determine what does and does not fit me from their offerings then it is useless to me.