I may not be the best person to answer since I have no kids and my wife was unusually accepting from the get-go, but here is my input...
First, you might want to ask a therapist/counselor for advice. They deal with big secrets being revealed between spouse a lot, and can at least suggest some ideas that often work and things that often bomb in a big way. I'd definitely have a therapist's number on hand in case things really do go badly.
Don't come out to your spouse and the kids at the same time. Once your spouse knows, you can decide together on how, when, and if you should tell the kids. If your kids are out of the house at the time (with a sitter, friends, etc), even better.
Don't do it on or near any holidays, birthdays, anniversaries, etc. Don't tell her right before work or before going out somewhere. Wait until your spouse is in a good mood; telling her when she is tired or felling grumpy is a sure recipe for disaster.
Even if she is supportive and accepting eventually, she may react poorly at first. Some spouses meet such a revelation with a hug and gentle words of support, but often the immediate reaction is a mix of shock, anger, and grief. Remember, you are basically turning her understand of you on its head; it will be a shock that takes a while to digest. Don't try to force understanding on her right away. You may get barraged with questions and/or accusations; don't take them personally, just respond honestly. Above all, avoid accusative language even if she is pushing every one of your buttons; it will only make things worse. Depending on her reaction, you may want to suggest seeing the therapist together for at least a couple session.
When you tell her, don't be "dressed out". She shouldn't see you in your "preferred mode" until after you've had a chance to explain it to her. If she asks to see you that way, fine...but don't surprise her with it.
No ultimatums, no matter how unfair you might think she is being about something. There will be things you need to stand firm on regarding your future rights, responsibilities, and behavior, but this is not the time to "put your foot down" on stuff. Disputed points are best negotiated in the presence of a qualified therapist.
All in all, hope for the very best and be prepared for the very worst.
Anyone else here have some wisdom to offer???
