Scale and Unit Problems

So I recently started working at a production plant where I was tasked with drawing the blueprints for a large facility. There was already a partial drawing that I built upon finally getting the whole plant. I don't have much experience with AutoCAD btw. So the drawing I worked from was already using units of feet and inches, so wherever I moved my cursor, the coordinates are given in feet and inches and from my research it seems like AutoCAD tends to be unitless when in Model Space. The Model Space itself is far too big, the farthest extent on the x-axis is over 1.5E+7' and the y-axis is just as far. So one question is how to basically make the Model Space a more manageable size. Also when I try to plot the entire drawing, using a plotter that uses 24" x 36" paper I cannot seem to utilize any appropriate scale. If I set it to 1 inch is equal to 10 units, which i would assume would be 1" is equal to 10', the plot preview is a miniscule section of the bottom left corner of the page. Any assistance is greatly appreciated and I can elaborate if need be. Thank you.