Question : 142 Hosts on a LAN? Too Much?

I *inherited* a LAN that contains 142 devices.

2 Active Directory Domain Controllers
11 Servers
6 Switches
13 printers
101 Windows Based PC's.
This is on one segment.
In addition to that we have a WAN with 400 hosts at 38 Sites.  

We have lots of mysteries on our network, which we are never able to solve, because everything is one big layer 2 mess(literally). It is a switch plugged into a switch, plugged into a switch all the way down  the line.

I have looked all over the internet looking for some sort of standard on how many hosts should be on a subnet, to support my suggestion that the LAN should be broken into 4 or 5 segments, divided by routers, but so far I have gotten nothing, and the higher ups just look at me like deer in headlights.

I hear a lot of CCNP's and net guys tell me I'm an idiot for having that many hosts/servers/DCs on a segment. I agree, but I need documentation and recommendations.

Any Ideas?

Answer : 142 Hosts on a LAN? Too Much?

The 3745 is a very expensive router that will become the bottlneck of the network. My suggestion would be to use a 3550 switch with L3 capabilities. Much faster, more ports, much less expensive, and provide all the features you're looking for.
http://www.cisco.com/en/US/products/hw/switches/ps646/index.html