You`re making this feel far more complicated than it really is
The answers to your questions . . .
1) You need to fill in a `Gen Dec` form with details of everyone on board. This needs to be faxed through to HM customs. Your airfield will probably do this for you.
2) Just speak to Le Touquet just after you reach the FIR boundary and don`t worry
3) The prevailing wind is from the sea, so the runway is usually 32 (or whatever the take off out to sea runway is). You will usually be asked to join downwind for 32. This is easy because the runway runs roughly parallel to a big river estuary. You can`t miss it
4) If you`re coming from the South East of England in a single, you will cross the FIR boundary about 15 minutes before you arrive at Le Touquet. Insert 'EET FIR BOUNDARY xx minutes' (xx being the duration of the flight minus about 15 minutes).
Whatever you do, don't stress about this. It's a piece of cake