I think X-Plane is max 1280x720 pixels, so if it fills more screen than that you have to crop it somehow. It fits the normal 4:3 monitor shape. As for as interface, not sure what you mean by that but I have a CHProducts 6-throttle quadrant, joystick, and rudder pedals hooked up to it and would not want to use it without those controls due to rapid response the program has to to inputs from the pilot. It really is a more dynamic sim than FS2004.
One thing you can do with it, and I tried this, is set up a network with a second pc running a second monitor. You can divide up the visual content to allow a split of the visuals and give half of it to the slave computer. It's a mess getting it all set up, but when you do you have an expanded graphic output. I had mine split up so the aircraft panel was mostly on the bottom and the forward view out the window was on the top monitor. I eventually gave up on it because the computers weren't evenly matched and the slower one couldn't keep up. The faster one had a frame rate of 60 frames per sec. and the old one would barely manage half of that which was distracting. It was neat to see all that graphic content though. If I had the money to buy 3 matched computers I might give it another try. For practice you only need one pc and I use it for approaches and not much else. It is not accurate enough to model computational fluid response without which you're basically guessing in any flight sim.