If you don't issue an invoice via PayPal (which is pretty common), your email address is the way payment is issued. Of the information requested, they don't need your full name, or your cell phone number (especially if they can't make calls). A reasonable response might be to offer to issue them a PayPal invoice instead. I think that in order to do that, they have to provide you with their PayPal email address. One of you has to know this if you don't work through a middleman (such as eBay).
There's not enough information here to actually hack your PayPal account, unless you've poorly chosen your password. If it's a scam/con, I'd guess they're hoping that's the case - e.g. a password based on your name, or public information related to you, such as the name of your spouse, kids, pets, information you give out freely on Facebook and/or Twitter, etc...
The other way they could do it would be to ask for some other additional information in a subsequent email that also would sound innocuous, but which when combined with this email would be compromising.