I am not sure about the L2TP - my guess is not. It sounds like you are trying to make the connection process easy to manage from a client perspective insofar that there is little or no installation required for a new client?
http://openvpn.net/index.php/open-source/341-openvpn-compatibility.html
You can push dhcp options to clients - but I am not sure this is exactly what you want (see url below). Do you want them on the same subnet as your remote network?
http://openvpn.net/index.php/open-source/documentation/howto.html
You definitely can setup different groups to have different access levels. I use the --client-config-dir option to point to a directory that contains configuration extensions based on the client that is connecting (you put files in the directory with configuration directives named the common name of the client - same as the name in their certificate). Combining that with a firewall on the server you can control access based on the client. If you need something more integrated, you can build these configurations when the client connects using a script.