How much bandwidth?

I love thought provoking discussions, and this one is a true to life scenario.......

So let's say you have 8 Mbps Down / 5 Mbps Up Business Class Internet connection and around 30 lightweight users, most of which are only accessing files via LAN and a handful (maybe around 5) accessing cloud apps constantly throughout the day. So essentially you have 35-40 users. Two questions:

1. Is this enough bandwidth?

2. If you have 4 users streaming audio from the net throughout your facility, how much of a hit does your bandiwidth take?