I came to Makuhari Messe for an event hosted by a Japanese client.
This area is a newly developed subcenter, so there are plenty of places to eat, drink, and stay. There's even an outlet mall nearby for shopping.
There are lots of hot spring hotels around Lake Kawaguchi. You can enjoy the beautiful, peaceful night views of the lake while soaking in an open-air bath. Definitely plan to stay here for a few days if you can.