for #1,3,4,5: the extracted files which come with the multisync.dll include some excellent example dbp files in an 'example' folder. they're well commented and show you how to set up both clients and servers and send files and data between. there is also a detailed command list which explains what is available, what they do, and how to use them.
LAN connections using local IPs are pretty simple and don't require to you mess with port forwarding or anything so that's a good place to start. I'd recommend not trying to setup an external connection over the internet straight off.
as for #2, assuming it's a basic peer to peer game setup, if a client drops the host will keep the game running without issue and the client or another can still connect/reconnect to it no problem. if the host drops, it's a bit bigger issue.
one way to continue the game would be for each client to be sent a list of the IP's of the other clients when they first connect then when the host drops and all the clients find themselves disconnected, going down the list, the next client would automatically set up hosting of a new game, the others would look up the next client's IP they had stored and attempt to connect to the new host. they should all still have the current data, state, and progress of the game and continue where they left off.
for a server/client setup, the server should be storing game data locally, outside of the game and if it goes down, the clients can just attempt to reconnect until the server is brought back up again. it can reload the stored data to set the new session back where it left off.
