The RFC indicates that on a RRQ the first block number should be block #1, but the lecture notes indicate block #0.

Follow the RFC - the first block of a RRQ should be block #1.

Am I right to assume that our TFTP server only needs to support file transfers with clients that can handle the change to another port between the request and the first answer as described in the RFC? Otherwise, providing concurrency would be difficult.

Yes, this is a valid assumption (and I don't know of any clients that don't support the change in port numbers).

I've never had one of my questions show up in a FAQ, and I'm trying not to feel inadequate. Is it possible that you could put a question of mine in the HW3 FAQ so I can feel as though I'm contributing?

No.