The first thing you need to do, before buying anything for the costume, is get to know the machine itself.
Pull out the manual and read it. Really.
Plug it in, turn it on, put your foot on the pedal and play with the stitch settings- before you even try to thread it. You can run a machine with no thread without doing any harm to it.
get a piece of paper and 'sew' it. No thread, just feel how the machine pulls the paper through, try some turns, try a back stitch. just get a feel for speed and power.
then thread it. Un-thread it and thread it again. Do this about six times.
get another piece of paper and sew it. this time it's real stitches, but still just practice paper which will give you a good bead on the machine.
NOW you can get some scrap fabric- just trashy stuff, nothing special! and do all the same things you did with the paper.
Fill a bobbin.
read the manual again.
try doing some real seams on scrap fabric( most patterns are designed with a 5/8" seam allowance). Your machine likely has markings on the sole plate (you know what this is because you read the manual, right?) to help you sew even seams.
All that should take about two hours, unless your manual comes with a video or something.
what you want to look for is:
the overall shape as it sits on your body (fitted, front opening, high to neck collar blouse, separate skirt)
major design elements (in this case, box pleats on the skirt, princess seams or darts on the blouse)
- use a top from one pattern and a bottom from another
- often swap one style of sleeve for another provided both bodices have the same sleeve type opening
- add details on he surface of nearly any shape
- remember not all drawn clothes have seams drawn in.