1. the ability to accept credit cards on the website. Therefore, person does not have to leave website ?
1b. for both paypal and authorize, or only one ??
For Authorize.net, yes. For Paypal, no. That would require Paypal Pro which we currently (plan to) do not support. Please note for onsite transactions you'll need SSL support (https) and a valid (not self signed!) certificate.
2. I believe you indicated you support authorize.net recurring billing (ARB ) ? Is this right.
Yes, ARB is supported for recurring subscriptions.
3. do you support paypal pro us ?
No, not at this time.