Instrument access: I have a flute (and my voice obviously) at school. I don't have my own piano but I have access to a bunch of music practice rooms with pianos in them. If I took guitar, I'd be bringing a guitar (probably acoustic) back from home over the summer.
As far as skill goes: I played the flute for all of middle and high school. I took piano lessons in elementary school but have since forgotten most of it. I've never had voice lessons outside of a music theory class, but I can pitch-match, and I can sight-sing decently if the melody is mostly stepwise. I've only played guitar a few times, but I've played bass guitar for a few years now. Edit: Also, I have taken a jazz (performance) class before on bass guitar.
Which music classes should I take?
Orchestra (2 semesters)
Voice lessons and piano lessons
Voice lessons and flute lessons
Voice lessons and guitar lessons