Hi Sam,
When I was researching gear ratios, I ran into a spec sheet for the Enviolo hub on my Charger4. You might find it helpful in answering the "how many teeth" question for the rear hub. Looks like 20 to 28 tooth sprockets are supported. Here is the link...
What a great analysis of gear ratios and cadence. I have a Charger4 Vario, bought 3 months ago. I found that the gearing was much too high. The Charger4 comes with a 55 tooth "sprocket" and a 24 tooth rear "cog"; giving a ratio of 2.29 to 1. Worked up a spreadsheet, and determined a 46 tooth...