The quickest and easiest way (in my estimation) to create a new drawing that will be accurate and to scale would be to draw all your objects to real size in Model Space. I set up DIMSTYLES and TEXT STYLES with the proper height to plan ahead for the scale that I intend to plot the drawing at. After you have drawn all the "stuff" that you want in your drawing, switch to Paper Space. Create a viewport and scale the drawing in the viewport to the scale that you want it to be. Now, when you want to plot the drawing, all you have to do is go to Paper Space and plot your drawing at 1 to 1. I even draw the border to real size and place it in Paper Space so that the viewport sits inside it. It gives a pretty good view of what your plot will look like.
I'd also consider setting up your existing drawing the same way. Place all the graphics in Model Space and create a viewport in Paper Space to the scale that you need.
Hope this helps,
Paul