First, I can guarantee there aren't any Adobe reps lurking in
here to sell you something - resellers, perhaps.
There are literally hundreds of installations in the 100-400
user range, so this scenario for 1 Connect server is well tested.
The licensing itself is also easy math, an upfront free for the
server, and a 20% M&S agreement for each year following. In a
lot of cases, a licensed purchase can be more cost effective then a
hosted in and around the 24-30 month mark, it all depends. The
server itself is just the platform, so to speak. You will need to
purchase licensing for meeting rooms, presenter licenses, etc.
Again, all of this usually beats-out a hosted purchase around year
2-3 because you're not renewing the cost of the products each year
in a licensed install, only the 20% M&S.