I would like to setup a RaspberryPi "Home Server" + XBMC. I would install services such as SSH Server, VPN Server (openvpn or ppp), DLNA Server (miniDLNA), SAMBA Server and Transmission-daemon, all of them running 24/7. XBMC would start only when i press specific button on tv remote (TV connected by HDMI, CEC available). Is this setup possible? What OS should i use?! Raspbian + XBMC, Raspbmc or XBian?
I'd go with @lenik's comments and have two. I tried to use an XBMC distro to do extra things and it struggled under the load. Additionally, there's a chance that as you play around with it to get all the other services running, you might just break it (like I did!). If anyone else is relying on your RPi for their entertainment, they'll be severely disappointed.
Why not run
OpenELEC on one Pi, which is designed as a stand-alone appliance and therefore not that easy to fiddle with. Then get another Pi for your server and install one of the mainstream distros on it. You could network share the media between the two Pis.
Yes, you can do it. The more services you add, the slower your systems gets. Do you really need all of this?
The easiest path is Raspbmc which already includes many of these softwares. I also recommend to buy a good quality SD card and source power supply if you will let it on all the time.
For the remote control, take a look at lirc project.
If you have any further question, let me know.