VBA serial I/O via COM to my I2C device

In VBA, if I treat the USB to I2C Converter with Virtual COM Port FT230XS as a COM port, send my device commands in “API Encoded Format” to the COM port and then get the input & replies, is that all there is to it? That would be great.

That is correct. Just write the commands to the port as byte arrays and responses will be returned over that same COM port.