I think we can handle matters out of court - when we spoke about it, there's no desire on either side to screw over the other. Neither has committed adultery and nor has there been any physical or mental cruelty. That said, I'm not complacent and it's something I'll investigate.
The problem is that women can quickly go from "I don't love you any more" to "I never loved you" to "you wasted the best years of my life and you owe me everything to make up for it". You need to cover yourself for when she finds she can't hang on to "her" house. You also need to get any financial settlement sorted legally, as otherwise (as recent court cases have shown) she can come back at any point in the future and claim your income. This is more likely to happen when she realises that she can't cope without you pulling in more money for her to spend.
I'm not sure what I can add to the already good advice you've been given. I do think maybe she is having some kind of mid-life crisis, and despite charming your wife's family, the friend will have been egging her on in that direction. The friend obviously wants your wife for a partner in crime so that they can be divorcees together, living the single life. Your wife may not have been cheating, but she obviously wants to get out there with her friend and start looking for someone new. I think you made a mistake in ignoring the issues you've been experiencing as a couple over the last 18 months, but now your wife has decided she wants out, there's not much you can do about it. She's checked out of the relationship. As you've said, the person you knew isn't there any more.
I do think you will be okay. You seem to be more self-aware than most men. You understand your emotional state and what you need to do to shore yourself up (reconnecting with family and friends, severing from your wife and her family), and you are moving quickly to anger as a motivation to move on. You also seem to be task orientated, planning the details of the break up and executing without letting your emotions drag you back. The decision to let her take the dogs was a brave one that shows your determination to cut yourself free of the past. I would imagine (from your walls of text) that you tend to over-think and over-analyse things a bit, so keep busy so as not to start your thoughts circling around the breakup, what you could have done differently, etc. That's all in the past now, and you need to be thinking of the future.
Don't stress too much about those times you get upset and emotional. It's just part of the healing process and that you understand your feelings better than most. You have to go through the upset, stress and healing of the loss of your marriage and the person you loved, but there is light on the other side. You can see that from all the similar stories in this thread. If others can do it, then so can you. You can carry on with a new phase of your life, do different things and meet new people. First you need to deal with the details of the break-up, paperwork, lawyer, splitting of assets, then you have to move on and cut out all contact from your ex. Make a list, work through it, don't get pulled back into the past and what might have been.
It's a shame that things have happened this way, but this is what you have to deal with, ie, life as it is, not how you'd like it to be. To misqote a meme, you're losing someone who doesn't love you, she's losing someone who loves her. She's the one losing out here. Now you have to work towards your goals and get back to being in a place where you are happy with your life. You've already seen how people are there for you if you need them (including all us anonymous internet nerds in this thread). Don't be afraid to take their help, you might be returning the favour one day. They will want to help you get through this difficult time, because these friends, colleagues and family all love you in one form or another. For the sake of a bit of time and empathy, all of us want to see you get through this and be okay at the end of it.
One day you will look back and although the ending was bad, you had all those good years, and maybe you'll move onto something and someone better. This may be an ending, but it's also a new beginning for you and you have to look forwards into that new life, and forget about the past you can't change.