I'm glad to hear you have a plan for your husband's big step. My experience with my urologist/surgeon is that she had a drawer of assorted pads and adult diapers on-hand. You may wish to see what the situation is when the catheter is taken out and ask the doctor if you may just use what is in the office beforehand. My surgeon gave me an adequate pad in the office. My wife had previously purchased adult diapers and I never used them. I found the large "Poise" pads my wife purchased later were just fine for about 6 weeks, and then I could go to a smaller pad.
Everyone's experience is different and it would be a shame to spend a lot on pads or diapers that you don't need until you find out your particular situation during the first couple of days off the catheter.
Just my two cents worth
You and your hubby are in our prayers.