Plans and how to's arrived yesterday

Weather I go with Wadefish or Sabalo I am looking for lightest possible build.
I realise the type of ply I use will effect this outcome so I probably will use Okoulme or Gaboon, as yet I still have to find a supplier, I live in Sydney Australia its a fairly large town.
My question is this I noticed that Danger Mouse added a lot of extra holes in his cockpit framing,the how to's say don't do this?
Is this because people could cut to many and weaken structure?
Is there a layout for lightening holes or is it just a matter of common sense?
My gut feeling is use common sense but I thought I would fish arround a bit.
