No need to include your wife's name as she is not a member.
Email every time in my opinion email@example.com
You will receive no more attempts for contact than via a paper source.
This is an administration process. There is no need or added value to the process in including a lot of reasons why you are resigning. Keep it to your personal administration details. You will need to include a postal address if you wish them to be able to contact you via a letter.
Sometimes depending upon the country a differing response may occur with regards to what letter you may actually receive.
Know that the procedure is still that a bishop needs to confirm you are not being forced to resign against your will, he will be informed from membership records following them receiving your email, and then he emails the SP after he is sure and then back to membership records and your name is removed. But there seems to be an increasing number of cases where processing for resignation is occurring straight away, all the time the procedures are being streamlined and made more efficient. poc will say they do not like to look like a cult by making it hard for people to resign.
So I can not say exactly what will happen but you can check you have been processed resigned after about 6 weeks in a snazzy way if you still have your membership to hand. Just try to set up or access your lds account on ldschurch.org. If it does not work, you know you are marked name removal.
The board is here to support you every step of the way. You need have no concerns about that.