Yes, it does has limits. It’s better to use tools like SalesHandy or Yesware.

yes Right inbox and salesHandy are great tool scheduling emails with different time zone.

Gmail will not allow sending mass emails. You can use tools like saleshandy which allows you sending emails to 200 contacts at a time after every 3 hours.

use SalesHandy tool to send personalized bulk emails. SalesHandy mail merge feature allows sending emails to 200 contacts after every 3 hours.