[Meizu M2]Boot to stock recovery: flashing firmwares, recover from softbricks etc

First of all: the primary language of this community is italian, but I wanted to try an English thread to test whether or not we could recall people from other countries, being this one of firsts subforums dedicated to our beloved Meizu M2.

This thread is being updated, I'm still gathering information. If you wolud like to help (even correcting my poor English) you are welcome :)

I open this thread to help anyone who will experience bootloops, softbricks etc (it's not yet happened, but nobody knows..)
The firmware of reference is 4.5.3.1A

Answered questions

0. what ca I do from stock recovery?
Here, you can perform:
-Factory data reset
-Flash of original meizu firmwares (downloaded from here FlymeOS????-??2)

1. when can I enter recovery?
You can always enter recovery if your phone shows the boot logo and you have a decent amount of charge in your battery (you don't want your phone to power off while flashing...want you? also, entering recovery with less than 20% battery, a message will pop up asking you to reboot the phone and come back with more charge)
In recovery, you can move in the menus using either the volume rocker or the touchscreen

2. how do I enter recovery?
It's as easy as that: with your phone already powered off, press (simoultaneusly) vol+ key and the power button until the phone boots. Note: if the phone could not be shut down (phone not responding at all) you can shut it down/forxe it to reboot holding the power button for at least 7 seconds. Then you should be able to use the vol+&power button combination to enter recovery

6. can I upload the update.zip file via usb with my phone already in recovery?
Yes. With your phone in recovery, you just have to plug your phone into your computer via usb to get it detected as an usb pendrive (an empty one). In this "pendrive" you have to copy the firmware you want to flash. Once copied, remember to perform the safe removal of the device before unplugging it (from windows->tray icon of the usb stick-> eject MT65xx): you don't want your file system corrupted in this moment, I think

Questions to be answered

3. From recovery, can I flash A firmware over U,C or Q? what about U over A,C or Q etc?
4. Do I have to reflash the rom I already have or can I flash a newer one? If I can flash a newer one, does it have to be the same letter (A,U,C or Q)?
5. Can I downgrade my firmware?
7. Can I upload the update.zip on an sd card and than flash from it?
8. How long does a firmware flash take?
9. Is it true that if I catch all the unowns something happens?