Follow up (if someone else is in the same situation) First of all I should make it clear that before all this the entire thing WAS already working with different VPN server so... I created an IP...

Just bouthe R605. The main network (DHCP by the router) is in range 172.16.0.1-200, VPN IP pool is 172.16.1.1-50 - not the same subnet as required by instruction: Instruction. Setup L2TP, User:...