Aaaargh I just checked, you had said sunday 12th september! Damn french!
I can't be there then... I promised to be good and do some work at home so I could leave early on sunday...

What to expect: mostly fear during the 20 minutes it takes to the plane to reach 4000m (everybody feels the fear, after 25 jumps I still have a bit of it when the red light goes on and the door opens) then sensory overload when you exit the plane.
Thanks to the adrenalin you won't feel the cold (it's around -10°C up there) so no need to wear more than a T-shirt and a pair of pants under the jumpsuit. A light fleece if you're always cold.
You won't have a real sensation of falling because you exit the plane with a horizontal speed around 160 Km/h (lot of relative wind already). When you reach the terminal velocity (~200 Km/h), you'll have the feeling to float as you don't accelerate anymore and are carried by a cushion of dense air...
The first time I jumped I held my breath until 2000 m such liquid-like is the feeling.
Listen to your TM during the short briefing and do what he or she says/points you to do (it's impossible to talk during free fall). You should naturally relax as soon as your stabilized after 5-10 secs of free fall...take your time to look around
Then enjoy the canopy ride. The TM should let you play a bit with the toggles for a moment. Oh yeah, again thanks to the adrenalin this is the moment when you'll feel the pressure in your inner ears. Just swallow a couple of time without breathing like you do in a plane and they will equalize.
Last couple of advices: on final, when the TM says to lift your legs up, DO IT! Don't try to brake the fall qith your feet or land yourself first. Some people injured themselves while doing this. Trust your TM and let him/her slide the both of you smoothly on the grass.
Wear sport shoes (running shoes are best for this) without hooks. There is a very little chance that a hook could snag a line during canopy deployment, but if it occurs the scenario would then be ugly...
Enjoy and keep us posted.

Bonne Merde!