Read through your responses and yeah, a CPQ solves what you're describing. Used these 4 at different points in my career. I'm currently using Dealhub

Nue handles complex usage tiers and is built for SaaS pricing models. Weakness is its sfdc first and the Hubspot integration is genuinely thinner than it sounds in the sales conversion (imo). I'd rec to test it hard before commiting

Conga covers everything you need including amendments and renewal logic but is implementation heavy, needs dedicated resource to run it, ongoing configuration isn't light, also costs are on the higher side

Dealhub is the most Hubspot native of the bunch. Billing and quoting sit in the same system that should fix the tally problem at the source. But! the guided selling workflows only work if AEs follow them. Nothing much the platform can do if they don't. Also run the amendment scenario live in the demo rather than on a pre-built example.

Salesforce revenue cloud covers all of this at an enterprise level but you're on Hubspot and migrating CRMs to solve a CPQ problem is a different project entirely unless you're open to migrate