Sending Group mailing is a very good way to welcome your new PSAs, But sending each one a individual E-mail is more warmer and makes your PSAs feel more wanted.
Also by sending a individual e-mail your new PSA is more likly to get it for it will be
right in his or her personal mail.
Your PSA is more likely to feel that if they need help you will be right there for them. Yes sending your PSA a personal e-mail is really the way to go along with your group mail.