You can seen below my little interfacing experiment. The envelope calls for medium weight interfacing, but that's a little subjective for my liking. I asked for medium weight interfacing in the shop but as soon as I got it home I was beset by doubt, it felt rather papery.
Here are non-interfaced, light interfaced and medium interfaced fabric squares.
So off to buy what I would call lightweight interfacing instead. Interestingly on the roll it said lightweight but I've just noticed on the receipt it says medium. Go figure!
In case you are still reading its Vilene F220, which is wider than the pattern calls for so no need to piece any of the interfacing pieces - hurrah!
Anyway, its going together well at the moment. I've made the front already. And it sort of looks like its supposed to.
Some lovely people at pattern review suggested that perhaps my muslin looked a little big.
The problem is I'll have a lot of sitting down to do during the day, I've experience a dress that looks lovely when standing but is too tight when sitting before and it rather spoils things. So I've cut it out as I planned but I think I'll take generous 5/8" seam allowances to reduce it a smidge.