More answers:

40 EUR for A7 Extra -> A8 Extra: Yes. A8 Extra -> A8 Com is not available yet.

Difference A7 <-> A8 in shadows: A8 stencil shadows are accelerated, and A8 will additionally support PSSM shadows.

Upgrade to A7 Com after March: Yes, you'll get A8 Com for free when you contact Support. Maybe you have it already, check your key.

Zahlungsvarianten: Paypal oder Überweisung. User ID/Passwort ist nicht nötig, der Name genügt.