That’s not correct. I have a 100 A ‘Shop’ c.t. in my hand and the opening is 12.5 mm (½" in old money), but 12±0.3mm on Echun’s own data sheet. The 200 A one is listed on the Shop page as 19 mm and as 19.4±0.5mm on the data sheet.
You also need to bear in mind what @Bill.Thomson has written about the actual current demand of the US 200 A service: US 200 Amp Service explained or Do I need a 200 Amp CT?
Other than that, you are generally on the right lines. I’m not sure whether The Shop will offer a US version of the emonVs with only two voltage inputs, because you don’t need the third one. You’ll be pleased to note that the pesky “USA” calibration change will no longer be needed.
The “Use in N.America” page will be updated when time allows (even though it isn’t and never was specifically for the emonTx V3). All the c.t’s mentioned on this page will be suitable provided the 333 mV version (where available) is requested - in fact, any 333 mV output c.t. should be suitable, though you will probably need to determine the correct value to enter for the phase error, as it’s not realistic for us to evaluate or check every one available.