Hey Tdubs!
See you on the 15th! Sounds like a very small class.
For the tie thing.... My first invitation to interview was in Jan, it had the business casual note. My second after Jan cancelled, for August interview had no note about a dress code. I don't know, but maybe it is because it became such an issue that they got sick of what do I wear calls to HR, and they dropped it?
Just me, but if there is no mention in the letter I would wear my best suit and tie, worked for me.