If you have emailed with him and you are going to attend the visitation, I think that is adequate. Continued outpouring of sympathy might appear ro be "groupie" like or peeling back a scab that is healing.
I would send a card and even reiterate some of your key comments from the email in it. You can start by saying something like, "As you already know...". IMO, it will make it easier for the husband to keep a collection of cards rather than having to save an email or go to the work to print it off and keep it with the cards. There may be times in the coming days, months, and years that he'll find some comfort in reading those cards and your sweet words will be a touching reminder to him of how others loved his dear wife.
I’ve recently been sending actual “thinking of you” cards at times after a loss. There are beautiful cards in the stores, and sometimes very helpful encouragement for the grieving.
Gentle thoughts to you as well, as you experience her loss.