G, lighthouses sound like fun, and you already have all of the serial
numbers you'll need in your pocket. When you contact your first
lighthouse, you give them serial number 1. When you contact your
second lighthouse, you give them serial number 2..., etc.

As far as speed goes, Morsemen are kindest and most helpfullest
amateurs of all. If they forget to match the speed that they were
called at, you could send to them "QRS" and they will get the hint.
Best of Luck, bb