for the code... sorry i can't post this one. It's prop to a customer but i remind to see some example here... do a search and you'll find them

Yes you can skip the INT pin and read the EOM instead, same for RAC.

I used them to make things simple and retrieve the begin and end address of each message.

ISDs chips are close to be great, the only kind of bug if those 4002, is the pop sound at the begining and at the end... wich can be resolved in hardware... one reason of the RAC and INT.

You don't need to bother about the SCLK frequency... it will work. It's a synchronous communication, not like a simple SERIN/SEROUT where the baudrate is important.