Can anyone recommend anonymous/tor e-mail services to use while doing direct e-mail deals with vendors?
Can I just use a regular clear net throwaway because I will obviously be encrypting everything anyway, or should I use some kind of Tor/Onion e-mail service?
No. That will link your home IP address to an email account that is sending encrypted messages to a known vendor.
Yes.
SIGAINT has a free webmail service:
http://sigaintevyh2rzvw.onion/