I don't think you are ever totally ready. At some point you just have to jump in and trust the water will be fine. If you find it's not, then get out. No blame, no harm, no foul. Stick together no matter what.
One of our first meetings was with a single male. We had a drink then went for dinner. During drinks we both (the men) kissed my wife, not aggressively, lovingly. My wife broke the ice by kissing him gently upon meeting for the first time. It was a signal to him and my opportunity to kinda feel out me reaction.
The night was more like getting in the pool using the stairs. First one step, water up to our ankles ( a few hugs and a few kisses), then the second step, water to our thighs (dinner with touching under the table and flirting). Her between us, us both touching her thigh, inner and outer. Third step more obvious and daring. Him kissing her at the table, then I, fingers inserted into her. Folks around us we're certainly interested in the beautiful woman and two men. More petting etc. The whole evening was a build up to the sex. It was so fun. At any point along that path we could have easily stopped and left. But in our case, we finally jumped in and loved the evening. Good luck.