The finish line should be short, typically doesn't need to be wider than a gate. If the starting line is long because of a big fleet, the finish line will appear dramatically shorter than the starting line.

Lots of things to consider of course... Upwind vs. downwind finish, spinnaker classes, wind/wave conditions, size of the fleets, how many you expect to finish at once, etc.

Separate start/finish line is definitely becoming the favored way to go, keeps things moving rather than waiting for all boats in all classes to finish before starting the next race (assuming no wild course changes are needed). People need to be reminded not to park on the finish line, though...

Mike