This is a solid approach. I would avoid using GA if you want to include email addresses though, since this will violate their terms of service as it relates to PII.
You might be over-complicating things though. Unless you want to track email opens, all you need to do is turn on Google Analytics tracking in ActiveCampaign Campaign Settings page (the last page when you create a campaign).
This will automatically add the correct utm_ parameters to the emails consistently.
Then just make sure you have Google Analytics enhanced ecommerce turned on.