I’ll answer some of the questions. Most if not all other questions actually are answered in the various unbricking threads (and there are a number of them). Problem is some of those threads end up discussing a variety of issues or My Cloud models and the core unbrick information gets lost in a huge number of posts spanning many years. Most people want something simple and don’t want to spend time reading. This isn’t something simple even though it is usually fairly straight forward process to unbrick once one understands the process.
The directions to unbrick a first gen My Cloud is different than unbricking a second gen My Cloud. Firmware v3.x and v4.x is for first gen. V2.x is for second gen.
Depending on which unbricking process you use will depend on which image (img) files you will need to use and which steps you use.
Personally I’ve used the Fox_Exe directions (there are a set for first gen and a set of second gen) to unbrick a first gen single bay My Cloud.
I have used Fox_exe’s first gen directions to unbrick and successfully use a 250GB, 320GB, 500GB, 1TB drive from both Seagate and WD. I have also unbricked a 8TB WD Red drive to work in a first gen My Cloud. Just unbricked a 1TB drive yesterday as a test bed on my first gen to work on the Clean Debain on My Cloud rather than using the WD firmware.
While you can use just about any type of SATA hard drive in the My Cloud, because the device is designed as a NAS it is recommended to use a NAS quality drive like the WD Red which may have better tolerances for running 24/7 with high usage rates over much cheaper desktop (WD Green or Blue) drives.
The various unbrick directions are generally not written for novices/noobs. Most assume the user has some knowledge of using Linux and will actually read the directions carefully. One reason for making the assumption that one is knowledgeable about Linux is due to the complexity of the unbrick process. And for the possibility one could target the wrong drive during the unbrick process. Unbricking or changing the hard drive on a single bay My Cloud is (obviously) not recommended by WD which is why one is on their own and responsible for any damage to their drive (My Cloud housing) or computer when performing one of the unbrick methods.
The main Fox_exe repositories for multiple My Cloud models can be found either here:
https://fox-exe.ru/WDMyCloud/
or here:
https://drive.google.com/open?id=0B_6OlQ_H0PxVRXF4aFpYS2dzMEE
First gen directions:
English: https://fox-exe.ru/WDMyCloud/WDMyCloud-Gen1/Replace%20HDD%20-%20English.txt
English: https://drive.google.com/file/d/0B_6OlQ_H0PxVbzZac0plbkZKeGM/view
Russian: https://fox-exe.ru/WDMyCloud/WDMyCloud-Gen1/Replace%20HDD.txt
Russian: https://drive.google.com/file/d/0B_6OlQ_H0PxVakNZMjFvdzloRVk/view
The img files needed for the first gen Fox directions can be found in the WDMyCloud-Gen1/Backups folder in the main Fox_exe respoitory link above.
Second gen directions:
English: https://drive.google.com/file/d/0B_6OlQ_H0PxVQVhnLVJOdDZISUU/view
English: https://fox-exe.ru/WDMyCloud/WDMyCloud-Gen2/_Unbricking_en.txt
Russian: https://drive.google.com/file/d/0B_6OlQ_H0PxVazVOdWNSejFXV2s/view
Russian: https://fox-exe.ru/WDMyCloud/WDMyCloud-Gen2/_Unbricking_ru.txt
Various files used in the second gen Fox_exe unbrick directions can be found in the WDMyCloud/WDMyCloud-Gen2 repository.
I cannot stress this enough. Which ever unbrick method you use it may/probably will involve some massaging to get working due to a large number of variables that the writer of these directions cannot control (Linux version, user knowledge, hard drive size, etc.) READ the directions carefully several times before attempting to unbrick. Don’t be surprised (mad or frustrated) if you have to run them several times before it works. Most of the directions are, believe it or not, straight forward (after one does it one or two times) even though it appears daunting to a noob/newbie.
Above all, do not expect to have simple directions. This is not a simple procedure. You are modding a product in a way it was never (officially) designed to be modified or fixed. It is up to the end user to take the initiative and do some learning rather than sitting back and having someone else hand everything to them on a silver platter (so to speak 
). All of us who unbricked for the first time stared from noob unbricking status and had to learn things along the way that may or may not apply to other’s when they unbrick.
If one successfully unbricks their single bay My Cloud it should boot to a blue front LED. If you get a red front LED, don’t panic. Try accessing the My Cloud Dashboard and performing a Quick Restore (Dashboard > Settings > Utilities) which may fix the red front LED. Generally it is advisable after an unbrick (what ever method you use) to perform a 40 second reset or a Dashboard > Settings > Utilities > System Only reset.
Finally one can find various past firmware at the following link with directions on how to downgrade if needed.
Edit to add: It will be very difficult and time consuming (not to mention possibly expensive) for someone to write up a set of directions that is easily readable/understandable across numerous languages (for example user Fox_exe is, I believe, Russian) and across various user skill sets. Keep in mind people who have provided information here are doing so on their own free time and are not being paid to assist others or write up extensive and detailed directions. If they do help or assist, they do so because they want to help their fellow man/woman and are doing so at their own time and expense.
