Yes, that's exactly how you add artillery to your ship - of course, the room
property has to be set to an existing and unocuppied room, like any other system. Start
property also has to be set to true. Also remember about an additional mount for the artillery, though it'll work even without it (though it'll look funky)
And no, you won't screw up anything. Artillery cannot be bought at store.
possible that your ship is just too big - while there's no size limit that I know of, there is
a position limit on the left side of the screen and to the top of the screen - and in the editor that limit is presented in the form of the anchor (you had that right, the anchor is a 0,0 point of origin for the ship)
Anyway, what that means, if your ship is big enough, you won't be able to center it perfectly, because you won't be able to move it farther to the left.
Coordinates; it's exactly like in the regular Cartesian coordinate system
. X axis is left-right, Y axis is up-down. The perceived "facing" of the ship doesn't change the way the game handles coordinates.
As for what values to change in the .txt files, look here
. In this file you can modify the offset of the entire ship (distance between 0,0 origin and the room closest to it) and positions of doors and rooms, as well as their size. Hull image position and size data is stored in shipname.xml.
And it seems like it'd really help you to take a look at the documentation
that I wrote for the editor. It explains the purpose of the anchor, and how to disable the automatic removal of doors, among other things (Edit > Automatic Door Cleanup).
So, sparing you the read, in order to move rooms closer to the anchor you don't have to move them all one by one - you can shift-click on the anchor, and you'll be able to move it closer to, or farther from, the ship.