Hi Will - I'm sure others will chime in, but:
1 - yes, you must consult with a lawyer before moving out. If you stay in the same school district, that facilitates overnights with your kids. You can also have a signed and witnessed agreement on at least the custody schedule. But don't get "carried away" with agreements made without a lawyer, because some of them may not be enforceable and then you have nothing. Many people get into trouble with vague language about "generous access", "reasonable notice", and so forth. In my case, we just had a two-week schedule signed on the day I moved out, where I had 5 overnights out of 14, and immediately we started following it. The final custody agreement took six months, but the pattern was established right away.
2 - depending on their ages, your kids may know more than you think. Likewise, your friends, neighbors, relatives, and in-laws are probably not clueless. There are a lot of people who simply don't know what to say. I think on the day you move, you need not get into detailed reasons with your kids. Most people advise that you and the wife should make this announcement together. Each of you wants to know what the other says to the kids. You want to assure them that their needs will be met, they will not be moving (not right away, at least) and that you will see them regularly. This is a point where it's nice to have the custody schedule established. The announcement is quite a shock to them and will take some time to absorb. So you want to reassure them about whatever elements will remain stable in their lives. Do not argue with your wife in front of them during this announcement.
3 - Your wife might insist on putting out a sanitized version of the circumstances, but that's only to protect her. If someone asks you directly, be honest. And if you need support from someone close to you, by all means tell them. They've probably been suspicious already, and your separation will confirm it anyway. You don't want anyone, especially your kids, thinking that you simply walked out for selfish reasons. Yet that's the story your wife may promote. Eventually, you will end up telling everyone.
4 - Yes, a consultation with one of the Harleys is very helpful. It may be that you should try at least a short period of plan A first; you didn't say whether you had been following from the book or not. But regardless, the circumstances of beginning plan B are important; it's not to be a "punishment" for your wife's behavior. Another approach is described in the book "Controlled Separation", I can't remember the author's name but you can find it on amazon.
5 - Open up your own checking/savings accounts, and change your automatic payroll deposits to that account. Also apply for your own credit card. You should definitely cancel joint credit cards, but you might give your wife a short warning period. Also, you could take part but not all of the joint bank account balances, and leave the rest for her. So as not to leave her high and dry - doesn't look good to anyone. You should be able to document what you did, and let her know, don't leave nasty surprises.
There are some other financial planning steps to take ahead of time. First, most states calculate support payments from a formula, and you should figure that out ahead of time for budgeting purposes. You should even pay it regularly before the hearing, that way, you will not be far in arrears and have to make it up. The second thing, is to inventory your financial assets, including photocopies of titles, bank statements, credit card statements, etc., etc. Also make a photo inventory of the house contents (something I did not do). Assume that you may never be back in the house, once you move out. You could give your wife a copy of everything, so that you both have the same financial snapshot on the date of separation, and there is less chance of monkeyshines.
Ask your insurance agent if there are any implications of the separation on your policies. Ask your lawyer if earnings or gifts, post-separation, are still considered marital property.
Good luck ...
