At what temperature should monkfish be prepared?
To be perfectly honest with you, in all my years of cooking in kitchens I never took the temp of the fish.  It was always by feel and look.  Yes, I know that the gov't has guidelines that say 145F for fish but really when it comes down to it, if you have an 8oz cut of salmon/cod/monk in the pan, sticking an instant read into the middle won't do you much good.  (Caveat: If it was a salmon Wellington I would shoot for 130F as it's a fully enclosed package that you can't feel for doneness)

The thickness of the cut will make a huge difference in when you should pull it out as you get post-oven cooking during resting in which the heat continues to heat the core of the flesh up to a final cooked temperature.  That's why most chefs will take the roast out at a rare measured temp when they are shooting for a med rare serving state.

If your question is what state should monk fish be served, IE  med rare (like salmon) or rare ( like tuna) then I would say med-rare is your best bet.  Over cooking is a bad thing for monk fish and it goes from a lovely moist state to dry nastiness really quick.  A nice way to cook it that helps to give you a little move wiggle room when cooking it is to wrap it in Parma ham (prosciutto).  The little extra wrapping tastes great but also gives you a little bit of buffer as you get close to that magical temperature of doneness.

Hope it helps.