Thank's everybody.
I think I just install at first this client as unmanaged and check status weekly or so on. The server is running many important (heavy load) services so the extra load of the protection center was a good point.
External protection center was a very intresting idea if we could manage this external server (public IP without nat) from our office network protection center... But this sollution needs some time to configure.
Third thing is that I noticed that with managed client scans etc. are shown on standard Windows event log. If it is same with unmanaged client maybe I could send weekly those eventlog files from server to email somehow.