Is this only playable in DOS box? Seems like the screen size is either a small box in the corner of my screen or full screen and no resolution.

Press Alt+Enter, drag it to a center of your screen and play this OLD game in a windowed mode... :>

Any idea how you can change the size of the window?

alt+enter will change the game from windowed mode to full screen mode and back again

You can also edit the dosbox%.conf if you want and set your prefered resolution in windowsresolution=?x?.
You have to select an output other than surface for this to work.

Is there someplace I can find all the different options? Cause I have no clue what I could replace surface with.

Nevermind, google helped me there :)

The installer puts a "Graphic mode setup" shortcut in the start-menu folder. Just use that.
First, under Basic Settings, make sure it's not set to full-screen. Then, under Advanced Settings, change the Scaling Engine to whatever you like best - on my screen Normal3x is perfect. It may not be necessary to change the window Resolution setting.