in my opinion the best way would be to use your filemaker server as an IWP host, so your users will enter / edit / change data directly in the filemaker table via instant web publishing.
But - you should use a dedicated sever.
Using mysql, sqlserver, or any other sql database via odbc with filemaker would be second, no, third choice. Because large databases via odbc to filemaker are slow, veeeery slow.
Syncing, or replicating, my fourth choice. Because writing a replication mechanism is not easy. You must keep timestamp of last change, of last replication, and you must have a good algorithm to decide which side will overwrite the other.
greetings from gemany - hey, it would not take much and we were neighbours
did i talk about second choice? there is no second choice.