maybe 600 end devices (mixture of windows / linux / solaris)
net app filers
hp sans
networking is a vast mixture of kit
sites = about 15 (micture of datacentres and client sites)
Not too sure to what level some of the things you've listed there would be monitored - I'd give Solarwinds pre-sale a call and have a webex demo with them.
Tell them exactly what you need and go from there - prices are pretty aggressive atm - there's good deals to be had (IPMonitor now has an unlimited monitor license).