If he filed for divorce and you have been served you should have either his address or the address of his attorney. It is important that you file an "Answer" with the court. You can do this yourself but it is preferable to have an attorney do it. This is the best way to insure that you get some of the marital assets. you may also be entitled to some maintenance for your husband.
I strongly suggest that you hire an attorney who has experience in Petitioning for Guardianship of a minor. You may have to prove that the parent is unfit, unwilling or unable to care for the children if she does not consent to the Guardianship.
I strongly suggest you meet with an attorney with experience in family law matters to advise you on how best to proceed. If you wife obtains an ex parte order of protection from the court it may contain provisions that you cannot see your children and you must continue to pay the household bills until the matter is brought before a judge for a hearing.
Since you are preparing for a dissolution of marriage the last person you should take advice from is your spouse. I strongly suggest you get independent counsel who will have both your and your children's best interest at the forefront of the advice he/she gives you. Your attorney can request that your husband pay your attorney's fees when the petition is filed.
Service by Publication is allowed if you have exhausted other ways to find and serve the opposing party. You will need to file documents with the court proving that you tried to find him by other routes and then get permission to file by publication..