Either will work, but the reason Compact uses less resources is that it isn't a server. You would need to write some application or have a host process that can "open" the database file and work with it. Compact is essentially a set of DLLs that manage access to the files.

For replication, same thing. You'd need a process to run when connected to the network to update things.

Express is probably better if you want a simpler setup without coding.