Tokenised Email from external source - suggestions please


We’ve got a challenge and I’d love to hear your suggestions.
Our client’s (Business Network) built a website where a user (Member) can request a review from a Reviewer (either a Member or Non-member). The website sends the Reviewer an email with a link, the URL has a Token so the Reviewer can fill in the Review Form without logging in.
We want to enroll the Reviewer into a Workflow to:

  • ensure they fill in the Review
  • trigger Review Approval (Admin)
  • thank the Reviewer for completion
  • send reminders, etc.
    The Review Form URL includes a unique hashed Token. There will be more than one Token per Member and potentially more than one Token per Reviewer (therefore this excludes pushing the Token into a Custom Property into the Contact).
    How can we track the email open & click? And, trigger follow up events (emails, tasks, etc.).
    Problem 2
    The HubSpot Transactional Email system is over $1,000USD per month and it still doesn’t look like it will carry over the Token from email to reminder email… even if we did want to spend $100 per customer per email.
    Any advice would be appreciated.
    Workflow diagram available on request (it’s really a simple workflow with email, followup, approval but I find it easier to visualise in a flowchart).
    Thank you
    Thank you for taking the time to read this.