You'd be okay with the "basic front" instead of the "fitted front", the fitted one actually introduces more than you need with this costume. Once you have the basic shape, you just draw on where Sally's different pieces are - and cut them up and tape them together where they're one piece (like you have one piece that wraps front to back and don't need a side seam, for example).
You'd use a cheap fabric like muslin to work out the "bugs" and you could cut this directly to make the V-neck and other details. What I do typically is draw on the thing while wearing (or having someone else wear it) it where I want to cut - then transfer these differences to the pattern.
For modesty, you'll want seam allowances between pieces and clip the seams and press them and have the stitching seen be decorative. You'll want a decent weight fabric.