I'm starting, as I often do, from Kwik Sew 2514, with minor modifications:
- split the front center panel so the dress has eight panels rather than seven
- make the skirt floor-length
- flare the skirt out from just below the waist so that it will sufficiently full for ballroom
- add a sleeve
- add a float
- change the neckline
It sounds like a lot but I'm back in familiar territory so I'm no longer panicking.