I'm looking at installing a 2860Vac or 2860ac with 3 x AP900 and would like one SSID to be for Guests with individual Logon per Room , bandwidth and reporting etc
is that possible or better off with Ubiquiti AP or add an untangle Server

the don't do reporting, just a traffic graph per AP.

What does the Untangle do, isn't that subscription based?

Untangle is Linux based free with subscription additional modules
I've used it for 6 years now protects guests from each other and the Internet

have you ever tried running a Unix box and setting up Wifi Dog?

Not heard of it until now that is

Just got a Cisco Meraki and I have to say its very good.
Managed Wifi with "Facebook Wifi" login, Google login and custom pages etc
Reporting is excellent and the speed is brilliant