Avoid duplicates in Form Submissions and automate emails

I have a Subscription Form with mandatory Name and Email address fields. I have used the code to avoid duplicate email addresses using the examples posted before. I am facing 2 issues :
ISSUE 1 - Any other error like entering invalid email address or leaving the Name field blank only gives one error “Email Address already exists”. How do I differentiate between different errors?
ISSUE 2 - After clicking the SUBMIT button, I need to automatically send the new subscriber a “Validate your email address” email. How do I achieve this? I have tried the sendGrid tutorial but it is not working.