"It's going to be good music, good food and a good time," he said at the Yahoo! On the Road tour, where he performed in N.Y.C. Friday night.
And although they may be leaving many of the details up to the planner, the singer, 34, who will release his album Love in the Future later this year, says he does have a wedding song in mind.
"There's a song on my album that actually could be pretty good for the wedding. It's called 'All of Me' and it's inspired by Chrissy. She loved the song and cried when she heard it," he said.
Legend and Teigen, 27, who have been dating for nearly seven years and engaged since 2011, also says the couple envision a bunch of kids running around.
"We'd like to have kids. I grew up in a family with four kids, so I think three or four is a good number," he says. "We don't plan it. We just do it."