Dell Windows 8 Reinstall issue

Hello,

      I purchased Dell laptop (Inspiron 15 3521) two years ago with windows 8.0 home (pre-installed). After 6 months, I installed Windows 8.0 pro (what I had got from my office) and upgraded to windows 8.1 pro (Free up-gradation from Microsoft). Now I have to remove this windows (the license I got from my office) and reinstall the same windows 8.0 Home (what i had got with my laptop). But I am not getting any option for this. I do not have recovery disc. I tried to install fresh windows 8.0 home using disc but it failed due to wrong key in BIOS. I checked my dell account (System configuration) and found windows 8.1 pro as OS. This means windows 8.1 pro key has been registered in BIOS and due to this, I am not able to install fresh windows 8.0 home. Now the questions are :

     (1) How to recover my OS (windows 8.0 home)?
     (2) Do I need to purchase new license (windows 8.1 pro) now as I am not able to recover/install windows 8.0 home? I checked windows 8.1 pro installation is running.
     (3) If i install windows 8.1 pro and upgrade to windows 10 pro (Free up-gradation from Microsoft), in future, will I be able to downgrade or install windows 8.1 pro once again or will only have option to install windows 10 pro? Would i need to make the recovery disc for windows 8.1 pro?


Thanks,
Avitesh