Translated section of IP5306 datasheet: "IP5306 can recognize long key and short key operation, PIN5 pin is vacant when the key is not needed. ● The button lasts longer than 50ms, but less than 2s, it means the short press, short press will turn on the power indicator and boost output. ● If the duration of the key is longer than 2s, the long press will activate the light and turn it on or off. ● less than 50ms button action will not have any response. ● Pressing the short key twice within 1 second will turn off the boost output, battery level indicator and lighting LED"
It sounds like it will power up without pressing the power key, and that may be in the user guide when I zoom into screen shots of it, but I cannot find the pdf to download.
If I need to, I could remove pin 8 connection of IP5306 to allow simultaneous USB comms (without power) whilst running another 5V input.
MPU9250 uses the same pins as Grove I2C, so I think I will not be using that port unless some other 2018 versions do not have MPU9250.