Hi!
So the model causes the game to crush and shut down, right?
What?
This shouldn't make any difference. I edit often models in .mdx and they always work.
This depends on you. For buildings or ''static'' models (like tanks), the ingame camera works fine. If you use the ingame camera, it must have a stand animation named Portrait (it should only move like in the stand_1 anim). If it's something like a footman, bear or such, then i'd recommend you to make a portrait version of it. A portrait uses more space, but it makes the model more attractive, if it's a (generally spoken) an organic unit. Ingame camera and portrait anim are only fitting to buildings, tanks, siege machines, boats and such, as they won't move much in the portrait anim(s).
By the way: open your model in Magos. Then open the Texture Manager and look around for a texture named Replaceable ID 0. If you find it, delete it. Afterwards, open the Material Manager and check out each single material. If one of them uses this Replaceable ID 0 or no texture at all, then either make it use one (if any geoset uses this material) or simply delete it (if there's no geoset using this material). This is one of the most common reasons for making models corrupt.