Pfsense IPSec Server <–--> pfsense IPSec Client
Is it possible to host a IPSec Server with pfsense, and to join the IPSec VPN with another PFSense installation as IPSec Client?
If yes, is there any HowTos on the web?
Check the wiki. If all you need is to connect two locations via IPSec VPN then you set up a PFSense box at either spot and configure it. There are more details in the wiki.
Yes it is possible, enable on one side the mobile ipsec option, with 1.23 release dynamic to dynamic will be also possible
Dynamic DNS VPN tunnels work great in 1.2.3. I been running 1.2.3 for quite time with no issue.