I always ask for a physical description and age.. not because I have an issue with seeing larger gentlemen but because I want to know who I am potentially going to meet. I don't see many gents under 35 because of discretion issues but if they can pass my screening, then I make exceptions.
If he is larger, I would suggest he just mention it in his initial pm. Describe himself, what nationality, hair and eye color is good, weight and age. Then the provider can decide. And yes, ask him to shower thoroughly. The only times I've ever had issues with larger men is when they don't properly clean themselves. Nothing to me is more embarrasing than having to go grab a warm, wet, washcloth because it's not clean down there.