To have found this thread as DD got engaged last week. Her then boyfriend rang (they live overseas) to ask DH! Hoping this thread will provide lots of info for all of us. So far DH and I have said we “will contribute to the cost when we know what their plans are”.
Have a think now about whether you are going to be a specific sum (and tell them what it is) or if you prefer to pay for a few specific things (wine, flowers, whatever, and if you have a ceiling for how much you can pay, let them know that)
Beyond that, do not try to impose your views! Only give your opinions if asked for them. And even if they are choosing things you'd never do in a month of Sundays, make an executive decision early on that whatever it is, you like it.
We do have a figure in mind and think it will cover most of the cost, so will wait and see. We don’t interfere or give our views on anything unless asked - we’ve discovered over the years that we are often asked about things so seems to work!