Start working the doily pattern at whatever round corresponds to the point where 4 or 6 repeats matches your stitch count (you'll likely have to fiddle with that a bit, increasing a few stitches to make it work).
Hmm, I love the idea of using a doily pattern!
I'm not quite sure I understand how to make it work though... Say for example I wanted to use this doily pattern. I would start where half (if I were doing 4 repeats) the stitch count on the doily matched the number of stitches at the bustline?
Would I have to multiply the number of stitches in the lace pattern to make it large enough to be a dress since a doily is much smaller? Or, do I keep on increasing as in pattern until it reaches the desired width?
Say, for example, you are a thin woman using big needles and your stitch count just under the bust is 64 sts (completely grabbing that out of the air). Dividing it by 4 you get 16sts for your doily pattern repeat. Looking at that pattern you have 16 sts worked in row 30, so you would start the pattern from there.
Since you will be using much larger needles than you would be if you were knitting a doily you probably won't have to add any stitches. Most doilies are knit on needles around size US#2 or smaller. A lot of the vintage ones are on needles smaller than size US#0.
From the photo you posted of the inspiration it looks like there are about three rows to the inch. If you started the doily pattern on row 30 you would have 54 rows of doily pattern to knit, which works out to 18". You'll probably want to either find more lace patterns to add on to that one or find a larger doily (or table cloth, or circle/half circle shawl) pattern to start with.
Here is a nice big doily pattern and it also looks like you could easily repeat the lace pattern as many times as you needed to add length.
Looking at shawl patterns the curved portion of Innabun looks ideal for the skirt of a dress.
Herbert Niebling patterns might be a good place to look, though they can be hard to find. Most of them are large and designed for tiny needles so they might actually be too big knitted loose like that overdress. Frosted Ferns might look nice as a skirt, and it's free.