The Mansion is great for large groups. There were 7 of us and we managed to spread out amongst the bedrooms so we each had plenty of our own space.
It's a short walk to Leidseplein square which has plenty of bars, restaurants and coffee shops.
Getting to central is about a 20 minute walk but we did it a few times and it's always a nice walk!
Would definitely recommend for big groups looking to visit Amsterdam who aren't bothered about being directly in Central.