How to create a 'schedule email' feature?

My goal is to create a feature where our users can create email sequences and have them sent out at certain times. (think email marketing software like ActiveCampaign, MailChimp etc.)

How can I let the user schedule these in? Basically they would be creating cron jobs?
I need some thoughts on how to approach this.

So far I’m thinking:

1. User can create an email in our CMS, consists out of:

• Subject
• Preview line
• Body
• Sending date+time (they can’t set the ‘seconds’ online hours + minutes)

2. The user can fill this in, then it’s saved in the DB
3. I run a cron job every minute that checks if there’s any emails to be sent out at this date+time
4. Cron job sends emails to this user’s list

I’m not sure if this is smart, as this means there can easily be 100 000’s of emails to be sent in a minute. Let’s say a user has an average list size of 5000 people… this might be a huge burden on the server?