Is my information secure over public WiFi if I use a VPN service? i.e. protection of emails and login details.
Barring unforeseen weaknesses in protocols or implementations of your VPN service, this should give you a reasonable expectation of privacy. All of your traffic that traverses the VPN will be encrypted from your system to the VPN provider. At that point it will travel normally.
To your specific question of emails and login details, those should also be protected by this. Additionally, if you are viewing your email or logging in over HTTPS then your login details or emails should be protected through this encryption mechanism as well. Using HTTPS without a VPN will reveal more details though as not all of the connection data is encrypted (such as the website you are visiting).