USB data architecture ?

The data rates are fixed, as far as I know, as the receiving end has to synchronise to the data rate.

USB3 has nine connections (or possibly more with USB C connectors rather than USB A).
The extra five connections only connect with a USB3 plug and socket pair. Otherwise, just the four USB2 contacts are used.

The extra five connections are two data pairs for tx and rx, plus an extra ground / screen connection.

For USB1 or 2, Each data transmission uses a run-in or synchronising pattern 32 bits long, alternating for 30 bits then the last two the same, with the two data lines complementary to each other.
Then the data, then both data lines low to indicate end of data.

See here:

USB is a synchronous protocol so there are no start or stop bits just data bits. An entire frame will have a preamble and a frame check sequence. For more information get the USB specification or Jan Axelson's book.