Dude, trust me. I just graduated in may...and i had a 55g...what a HEADACH MOVING!
go with a smaller(2~29g), it's sooo much work moving it AND your appartment. But if your up to it, go for it, but you have been warned.
as far as tap water goes. it will work fine to "Start up" just dont top off or do water changes with it.
use chemi-pure, phospate sponge, and throw some de-clore in there and let the tank run for at least 2 days before adding LR.
i lived on the 3rd floor too, it was a headach, and a workout...but well worth it.
good luck.