Sam,
Please take a look at the picture and fill in the missing lengths where there are questions marks. I am going to assume the red box is a 4' x 8' sheet of plywood and will work off of those dimensions unless I am told otherwise.
Where do you plan to put the upper level? This is important as it can alter the track plan of the lower layout. What will be the function of the upper level? You might want to think about a shelf type upper level versus a large triangle.
This is a larger size layout and you will have no problem adding spurs, passing sidings and yards. I can see a large passenger station where passengers debark a train and then are whisked away to their homes on the trolley line.
What purpose does the layout serve (e.g. permanent, temporary, for you, for guests?) Are you modeling something specific? What accessories do you plan to include? Will this be a classic, modern or mixed type of layout?
With that long trolley line, you have the oppurtunity to spice it up with automated trolley stops.