This discussion is definitely a good idea. The following questions should help get the conversation started... and yes, there's a little more to talk about than where you'll start trying.
[ ] How many kids do we envision having?
[ ] How old is too old to have a baby? And how old is too old to have kids in the house?
[ ] If we got pregnant next month, what would we think? Yay? Yikes??
[ ] Are there things we desperately want to do or accomplish before becoming a trio?
[ ] Who's the first person we'd tell?
[ ] What lifestyle changes will we need to make when we become parents?
[ ] Do daddies (or mommies) do diapers?
[ ] Who's going to take care of the kids?
[ ] What's our response when people ask about baby plans?