Welcome to PMC Saiwha. You have a bit of a grand ambition there, not just crossing the channel but doing it at two or more miles high. I'd give yourself a bit of experience (actually quite a bit) before you think about that kind of undertaking.
For large water crossings you'd also need boat cover, emergency buoyancy and lots of other stuff to think about. If I were you I'd just focus on getting some training for now. Steve at Axis is a good guy.
A lot of people just go straight to PPG but you'll need to learn to control the glider before you add a power unit.
Whereabouts are you located?