How to begin?

My girlfriend and I have been developing the topic of cuckold relationships for six months now, and now we have decided that we will try to experience this in real life at the end of August. Finding a guy she likes is not a problem, but we are worried about one single thing - we would like the first meeting to take place with the three of us, together with me (in fact, we have even thought about the fact that I will be tied to a chair next to the bed and not I will have the opportunity to actively participate in their interaction). The problem is this: how can we ensure a situation in which the sex itself will go well and without unnecessary awkwardness?I’ll give you this example: my girlfriend cannot physically cum during sex, and therefore, after the guy cums, he will need to help her with his hands. Besides this, there are a few more subtleties that I learned over the course of a year of relationship, and the guy will have to learn literally in one evening. We really would not like to arrange their first meeting together (it seems that my absence will provide a more suitable atmosphere for them to “understand” each other), but at the same time we do not understand what other ways there are to discuss everything in advance, so that in the end the first experience It was a pleasant experience. It is also important that for the girl this will be the first guy besides me, so I would be very grateful to receive your answers, it will help us a lot! Thank you in advance!