OK - having taken everyone's advice into account along with my lack of VBA experience, here's my plan. Please feel free to comment if you think I'm making any howlers...
I'm going to create a simple form, content unimportant, and fix the width to a number of pixels to match the min screen res of my users by setting the form width property to e.g. "800px"
I'll set the form height to match that screen res by trial and error by opening and closing the database with as much other stuff removed as possible, using the shift key totoggle them on or off when I open and close it. If i can set a custom printed page size I'll use that as a preview.
When I'm happy with the size of this form I'll use it as a master to create new forms from (I assume i won't be able to use the wizard).
The one thing I'm not sure of is how to give the finished DB to my users so they see no traces of access and are just presented with clean forms. I want it to look like a pro database without access trimmings like the home menu or office button. It should perfectly fill the screen of users with the lowest res and for those with a higher res the forms should be centered and smaller than the screen