Paypal preorders aren't possible because SD doesn't charge until the beta is available (so ~8 months), Paypal takes the funds right away.

There will be a ~2 week window once the beta is released when you can use Paypal to preorder and get in immediately, though

Usually when the beta goes live you'll have a week or so to order using paypal.  Just keep your eyes open around that time.

You can't but it now, even if you used a credit card you wouldn't be charged until the day the beta is ready -- which is when you can use paypal