"The countdown's begun," Lachey, 37, told PEOPLE Saturday at a Hollywood event for The Matt Leinart Foundation. "You know, the clock is ticking, so we're getting dangerously close. That's all I can say."
His bride-to-be said recently she likes the idea of a winter-themed wedding, but Lachey won't succumb to pressure on revealing further details.
Still, the groom does admit to a little (understandable) vanity about the big day.
When asked if he's going to get in extra-buff shape, he joked, "I'm just gonna let myself go. She loves me for who I am, skinny or fat."
But seriously, he said, "No. Of course. Everyone likes to get in shape and try to look good on [his] wedding day, at least. So, I'll have to start hitting the treadmill regiment to get ready for it. "
Boys Will Be BoysWhile Lachey says neither the menu nor the cake has been set in stone, another important detail is definitely on his mind: the bachelor party.
"We're working on that," he says. "A few of the boys are here tonight, so we'll get some conspiring together and figure something out."
Sure to be involved in that event is Lachey's good friend Matt Leinart, who told PEOPLE at the event – which benefited underprivileged children – that the engaged couple seem meant to be.
"They’re the same people," Leinart says of the duo, who became engaged last November. "Nick is obviously a very close friend of mine for a while now. Nick is the ultimate guy's guy ... He loves sports. He's just very laidback and low key."
Leinart had equal praise for Minnillo. "Vanessa is beautiful and at the same time she can hang with the guys. And you know, she's an awesome cook." And since Minnillo's expressed a desire for children, Leinart is also happy to throw his support their way.
"I think they will" be parents, he says. "I hope they do. Friggin' A. I wanna be an Uncle Matt, you know?"