Of those three, I would recommend Ancient Runes. That being said, it's purely out of a personal bias that I make that recommendation as that's the elective I continued with. There might be some additional uses for Arithmancy if that is where your interests lie.

Most have learned to. The challenge is to enforce that you're not beneath them. You're not a secretary or a desk employee, and you must insist upon being treated as is your due. I'll not sugarcoat my answer for you — it is exceedingly difficult to enforce this at times. There are some men who simply refuse to accept the changing times. Thankfully, though, they are the few. So long as you find yourself a good mentor you'll do just fine.

I look forward to seeing you come through the training program in a few years.