How to keep insides of calzone from being too runny
Cook's Illustrated really has the definitive guide to making calzones which aren't soggy.  Since that one requires a subscription, check out Serious Eats recipe, which does not, although it doesn't have as much of the science behind making crisp calzone.

To summarize their points on avoiding water:


No eggs
Drain the ricotta
Par-cook and drain vegetables before using in the filling (e.g. blanch, squeeze out, and blot dry spinach)
Add a melty, low-moisture cheese like dry mozzarella or provelone below the ricotta
Cut 2-3 slits in the top and make sure they're open all the way


You can shortcut some of the work by simply using much drier ingredients.   For example, I've been known to make calzone with ricotta salata, which is dry enough to absorb moisture from other ingredients.

Also, if "as hot as it will go" on your oven is more than 500F/250C, you might turn it down a bit.