Hi
Is your library available using the I2C bus as I am only seeing usage using SPI.
I2C is supported, see the Examples and Wiki. Ensure to use HW_I2C if possible
and what is the difference between 128X64_NONAME and 128X64_VCOMH0?
VCOMH0 is a special setup to maximize contrast range if you use u8g2.setContrast command. However this is not supported by all OLEDs. Try to start with the NONAME device first.
Why only 512 bytes where I see some confs using 128 bytes.
Not exactly sure, what you mean, but u8g2 page buffer will use 128 bytes for your display (instead of 1024). Other bytes are used by u8g2 itself, by SPI/Wire libraries and by the Arduino environment.
Oliver