Obviously you would speak to your departure and arrival airfields, and N Coates require you to co-ordinate with Donna Nook. As said above, it may be worth giving them (DN) a call on the phone (Mon-Fri) as there may be no one there at weekends. En-route (and there's nothing wrong with going the scenic route if you want to
) you don't need to call the other agencies if you avoid their airspace - which you would at 3500ft. If you are more comfortable speaking to them - go ahead - although on a Sunday they may be on the golf course!
As a matter of interest The Wash AIAA is not active at weekends and only goes up to 3500ft.
As far as 'magenta lines' goes I'm with ShyT - planned correctly if it reduces the workload, gives you more time to look out the window and makes flying more enjoyable - why not? I've also spent too much time thumbing my way down a map with stopwatch somewhat faster and lower than you will be going!! Above all, keep a good lookout and enjoy!
