Also prefer matte - I find overtime, glossies pick up other prints and textures.

1000X1000 is the size in pixels.
I, personally, prefer matte photos, because sharpie rubs off easier on glossy. But you may prefer glossy.
I usually just send a picture from a photoshoot, sometimes of a still in a movie.
I have seen people get artsy on them, and get replies on the artsy photo!

And, yes! It's perfectly fine to tell them why you liked them in a certain role! I write that all the time!