I've been knitting a long time, and I still seem to restart many projects. It's almost as if I have to get comfortable with it before I can move forward.
I always prefer to use long-tail cast on, and when I have to cast on a lot of stitches (some times upwards of 350) I use 2 balls of yarn, one for each strand. I make a slip knot with the two and count it as my first stitch and then separate the two strands on my hand for the cast on.
If I don't use two balls, I always overestimate how much yarn to give to the tail on purpose so I don't run out. I'd rather waste a few feet of yarn than have to worry about running out. Then I have to make sure I don't start knitting with the tail :shifty:.
I guess what I'm trying to say is that knitting is not an exact science--it lends itself to flexibility and fudging when necessary. The mistake that glares at you isn't necessarily noticeable to anyone else.
If you need to cast on in the bathroom with the door locked, then do it. It'll give you the peace of mind that you at least got off to a good start.