Hi,
well, at first you will need to have a VPN I would suggest. If not you will need proper port forwarding. Take care to only forward ports from the IP your Kopano server has! A least it helps a little bit.
Regarding the ports have a look here.
When I started with UCS (some time ago…) I was thinking of a similar setup but due to the high risk of loads of ports to open to my local net I decided against. My suggestion would be to “buy” a second machine on hosted environment using it as a VPN gateway for UCS. Might not be perfect and not as cheap as before but it will increase security a lot!
Just my thoughts…
/CV