Puck, I'm getting to your question, I promise. I'm just being slow.
1. I'd say you are right, but I'm looking at Wikipedia for Percentiles, and the formula is apparently P/100*N + 1/2. This is the same as what you did, just with a +1/2. I'm not certain what the significance of that +1/2 is. If this is for classwork, I'd say look at your textbook and see what definition it uses. Maybe the +1/2 is there, maybe it isn't.
2. Yes, you understand it correctly.
3. Yeah, Q2 is always the median. How convenient! It's almost like statisticians defined it to be so