custom email to non-users, on a schedule

I need to create a single-table custom email that runs on a schedule (any time during the month 4 months after a date in the record).   

Each email needs to go to a non-user whose email address is a field in the record, and the text of the email needs to contain some other fields from the record.

I'm planning to do this in two steps:

1. Create a custom email (open, triggered on a record modification)

2. Create a pipeline to run once a month and do the record modification for the appropriate records - once the record is modified, the email will be sent.

It seems like this will work but I'm wondering if the pipeline updates would be considered "bulk" updates.   Since the recipients are non-users, the email must be specified as "open" - but I know there are issues with "open" emails with "bulk" updates - recipients could receive information that doesn't relate to them.

If this could happen, what is another way to approach the requirement?