Having moderate experience as the other guy, not part of the married couple, my point of view is somewhat different but:
1. She probably knows very well what the other guy is into, how he cums, etc. I was not warned the first time, but luckily I was not in the line of fire of her husband the first time out. Since then if he is about to blow I get away from whichever way he's pointing
. Honestly, you should just be able to say to the guy, "I'd prefer we don't touch each other at all and I'd prefer it if you let me know when you are about to blow to avoid any friendly fire incidents." Simple as that.
2. This is a team sport, the more enthusiastic everyone is, the better it will be. Love is not as important here in my opinion, it's just dirty sexy fun. But in a marriage, I can understand that can be more 'meaningful', and dangerous if you aren't mutually enthusiastic about it. The nice thing about your setup is that you to are both already on the same page, you want wild and she wants to get wild. Enjoy the experience, leave emotion at the door.
3. Good luck. No such luck for me, so I have nothing constructive to offer. If she isn't turned off by the idea, go for it.