1. This can be achieved by booting the rooted system image without flashing it. Then dump the whole MMC to a SD card and then copy it to a PC. The .bin file will contain all the partitions you can flash back.
Code:
adb shell
Leaf2:/ su
Leaf2:/ dd if=/dev/block/bootdevice/mmcblk0 of=/storage/(SDCardName)/mmcblk0.bin
Alternatively you can pull all the partitions separately.
Code:
Leaf2:/ $ ls -al /dev/block/platform/soc/4744000.sdhci/by-name
If you forgot or somehow lost the image I'm sure someone would provide it.
2. These can be flashed through Fastboot or ADB. If the device is bootlooping chances are high you can send a 'adb reboot bootloader' command to it. If that doesn't work you can flash them through EDL (I have to be honest the first time I ever heard about EDL was here 2 days ago)
3. The button combination you posted seems to work.
If for some reason it doesn't, you can always buy an EDL cable from AliExpress for €3 or make one. There's a 1 minute video on Youtube on how to make it called 'How to make EDL cable for Qualcomm CPU’s'