I think
Finnegan's a pretty comical name, to tell you the truth, i.e. not one that I could really take serious.
Finn is a nice name, but is getting very trendy among the trend-setting types, it seems. And personally, I prefer using surnames as first names only when the surname comes from the family.
As for sibling names, I like
Finnegan (
Finn) &
Eleanor or
Finnegan (
Finn) &
Jackson. I would not use
Sawyer with
Finn because of the overwhelming
Mark Twain association.