Whether or not I’d advise them to marry now or wait depends on the temperament of the couple. IMO waiting until both have graduated college and are ready to live together makes sense. Being apart can break you up whether you are married or not.
But I like where publisher was going with his list of questions. We got married in the Catholic Church and had to attend a retreat. There, we had a workbook and were forced to talk to each other about certain issues. Most of them we had already discussed, but there were a few we hadn’t. I can’t remember what they were now though.
Finances. Are both savers, spenders, etc. who will do the monthly bills? Keep things separate, joint, combo?
Religion. Is it a mixed marriage? How will they raise the kids - if they want kids.
Visiting families. What are the expectations for each side, especially during the holidays. And what if their ideas don’t match the parents/grandparents. How will that be handled?
What are their dealbreakers - the issues where they will end it ASAP or as soon as possible? (Physical abuse, addiction, affairs, etc) in Ann Landers, porn and cross dressing were popular issues too. Better to figure it out now.
General advice - respect the others’ differences. And you don’t have to like the same hobbies, but you should be supportive of them. You’d want them to be supportive of you.
There will always be good times and bad. They will always do something to annoy you, but then again I even annoy myself at times. Grit through the bad. It will get better (unless it’s one of the dealbreakers!)