GUI Button location issue

Hey guys.

Just started on the road to making buttons for my GUI, and I've already hit two issues.

These are both purely graphical issues, I've not started the functionality yet.

Basically, what I want to do is add a total of 21 buttons in my GUI, which do various things. The buttons should be positioned in the GUI and some I want to have a custom shape.

So, issue 1:

Can I make the buttons a different shape to the square one I'm getting at the moment?

And, issue 2:

The buttons aren't syncing with the GUI, they're syncing with the screen. So, when I resize my screen, the buttons move differently to how they should. Screenshots:

This is full-screen, and it's correct:

This is not full screen, and the buttons are now in the wrong place:

Here is my code. I don't have any packet/functional stuff yet, I've literally only started on the graphical side of it.

    @Override
    public void initGui() {
    	super.initGui();
    	buttonList.add(new GuiButton(1, 200, 166, 24, 16, "7"));
    	buttonList.add(new GuiButton(2, 200, 190, 24, 16, "4"));
    	buttonList.add(new GuiButton(3, 200, 214, 24, 16, "1"));
    }

Finally, for those who like to count, yes there is 24 buttons on the GUI. Three are just for show and have no use; just like a real ATM.