I resisted paperspace for a long time. Once I dove into it (help explains it well), it does make things easier.
But when I plotted from model space to a scale in the old days (and note: the previous process given you sounds good to me), I would determine the actual drawing plot area (i.e. if plotted D Size 24"x36", then I'd assume I'm going to get a plot area of 22"x34"). Then I draw a box around my model space objects with that aspect ratio. I size the box using the math of the desired plot scale (i.e. if I want 1:200 and my drawing is in mm, the bounding box should be 111,760x172,720 which is 22x34 x 25.4 mm/inch. x 200) The box also lets me see if, at that plot scale, my drawing fits reasonably at that scale and by moving the box around, you can arrange the objects in the box ( onplotted paper). Then if you plot "extents and set the scale, rob's your mother's brother. Once you are happy with everything, you can put the box extents bounding box on a layer that is set not to plot, so it doesn't show up.
As said before, the plot scale area in the dialog box is clear (you just need to get your mind arund it via experience). The Scale settings set the ratio of model space units on the left to plotted units on the right. The "Units" is tied to the entry above it and reflects the scale choosen above that. If you set a scale of 1:200 and you set the desired plot unites to mm below that, then 1 mm will plot as 200 mm and the units says "200" because that is the scale you set. If you say "Custom" in the scale, then set 1 & mm below that, then 200 below that at "Units", that would be exactly the same as plotting 1:200 for a specified scale.
As a QC, create a drawing only with a box at an even size, plot it, then measure it on the paper factoring in the scale to see if you got it right.
All this being said, nowadays, this is overly laborious. Paperspace simplifies the heck out of all of this. I'd advise you to get hip to it.