I can see it could be a good idea to have a full discussion about everything beforehand. My own experience of that first time was very much more a "spur of the moment" thing. But I do think it a very good thing that "Bob" will be with you. I think you'll find his presence a support and if you haven't had sex in front of someone else before you'll find that quite an experience, too. It may be that you'll find "Bob" gets real excited by watching - my husband certainly did. He held my hand that first time - whilst his friend was inside me. That was a reassuring thing but his excitement certainly overcame him as his friend sped up towards his climax and my husband urged him to "fuck her hard"... "cum inside her". So, you see, they can get carried away with their own excitement!
You take my best wishes with you, by the way. Have fun.