The VDDIO supplies power to the digital sector, mostly I2C, but it is a different domain and best practice is to bypass the analog (VDD) and digital (VDDIO) domains separately. Standard practice it to connect the caps directly to the MPU9250 pins and use a via on the other side of the cap to provide the connection to power. I would also tie ADO to GND or VDD, one or the other depending on which device address you want. If 0x68 is OK tie ADO to GND. nCS must be pulled HIGH to VDD, no bypass is required, for I2C. I would recommend you connect the interrupt to the MCU. The Pro Mini is one of my favorite MCUs but at best you will be able to get ~100 Hz sensor fusion rate out of it, not really adequate if your intention is absolute orientation estimation. My recommendation is to use 4K7 pullups if the number of I2C devices on the bus is six or fewer. If you have as many as 10 devices then 2K2 would be appropriate. I think the RESV pin is pin 20, right? Yes, I would GND this pin. here is one of my designs for reference: https://www.oshpark.com/shared_projects/WnZaoIHh BTW, the Sparkfun design is crap.