If it were a good friend and I trusted them and their family to "pull their weight" and not leave you in the lurch or out of pocket, why not? Could be a lot of fun
Obviously, there are plenty of pitfalls, not least, what happens if it is very wet and muddy.. could trash your garden totally if the marquee and walkways are not boarded etc BUT it could be a really laugh
Why not enjoy it? We had a marquee reception in a family friend?s garden and it was wonderful, relaxed and special. We hired posh loos, boarded walkways and the main marquee, put up a separate boarded out smaller marquee for the children and filled with table tennis, tv and video one end, lots of board games, small trampoline, colouring etc. so wet or dry they could go play away from the adults. All catering was external and I did the flowers with my mum the day before.
The land owners but the grass frequently for us and kindly cleared the farm yard up for a carpark. They had a great time too and really enjoyed being part of the day. Obviously we were careful about not taking advantage, consulted and asked them all the way, showed our appreciation in both verbal thanks and gifts etc.
Handled, well, I think you could really enjoy it