TCP sequence number question

Question

This is more of a theoretical question than an actual problem I have.

If I understand correctly, the sequence number in the TCP header of a packet is the index of th

Answer 1

The sequence number is not actually the "index of the first byte in the packet in the whole stream" since sequence numbers deliberately start at a random value (this is to stop a form of attack known as the TCP Sequence Prediction Attack).

No SYN is required, the sequence number simply loops back to zero again once it gets to the limit.