Hi George,
I have the same problem. Need a microscope to work on these things.
About the goodies on Aliexpress, it depends on your hobby. I play around with microcontrollers and well scopes, and for that the things like a CH341 programmer or a ST-Link are very handy. But availability is troublesome at the moment causing the prices to be way to high.
I will mark the measuring points for you on one of the photos I have, because there is no overlay with component numbers.
About the shutdown the 3V3 should go down to 0, but there is a small delay to allow the MCU to write settings to flash (original) or the SD card (mine)
Regards,
Peter
Edit: Attached the power supply part with voltages mentioned. VREF is not 1.25V but it is for measuring the battery level with the MCU, so it varies and is not to important. The 3V is missing on this picture, so another one is coming.
You might have to download the second image and zoom in to read the text.