Hello,
1. Yes, all 4 payment methods should be supported, but we didn't have the occasion to properly test the "debit" service as we are not located in Germany. Note that you'll be able to test every PayPal plus features using the "sandbox" environment.
2. You'll find attached a screenshot of how the PayPal plus payment selection page will be displayed at the last step of your checkout workflow, just before being redirected to the PayPal platform. After that customers will be redirected back to your shop with a thank you message displayed.
Best regards,
Mohamed Thelji.
Tsuki Dev