Not many answers, only some explanations on why the question was made.
BTW you managed to make the 14 questions only 13, now with reference to the newly numbered 13 questions:
1. It means that as everyone has been telling you there are DIFFERENT EFI and UEFI implementations and they may behave DIFFERENTLY.
2.Yes/no/maybe. (see #1)
3.Yes/no/maybe (see #1)
4.Yes/no/maybe (see #1)
5.No, you cannot install "grub4dos" to "MBR boot Code", you can install grub4dos (grldr.mbr) to the MBR and a number of following hidden sectors. You cannot install "Boot Manager" to "MBR boot Code".
6.Yes, but no, the MBR will contain only first sector of the grub4dos grldr.mbr, the rest will be written to following (hidden) sectors.
7.No. It will install "standard" MBR boot code. There are tens of "standard" MBR boot codes which function is to chainload the PBR/VBR of the partition marked as active in the MBR partition table..
8.When you do nothing you get nothing. The default is a "standard" MBR boot code", see #7
9.It is NOT POSSIBLE to "install bootmgr into MBR boot code", see #5, #6, #7 and #8
10.It is NOT POSSIBLE to "install bootmgr into MBR boot code", see #5, #6, #7, #8 and #9
11.It is a set of assembler instructions that cannot exceed 440 bytes in length and that are loaded by the BIOS when booting.
12.The MBR is by definition the first absolute sector of any hard disk like device, CHS 0/0/1, LBA0, 512 bytes in size and contining Boot Code, Disk Signature, Partition Table and Magic Bytes. getting here (already provided indirectly in Steve6375's answer) might be of benefit for you: http://thestarman.pc.../mbr/index.html
13. It is NOT POSSIBLE to "install bootmgr into MBR boot code", see #5, #6, #7, #8 and #9
Now I have read them carefully and even replied correctly to each of them, noting how 1/3 are duplicates/senseless, 1/3 are based on false base assumptions, the remaining 1/3 are about very basic mechanisms in the booting process, i.e. something that you should have already studied and fully understood.
Besides the already mentioned site:
Make sure to read additionally:
Once you will have read thoroughly the above, you will have the needed understanding of the BIOS booting process, with particular reference to grub4dos and BOOTMGR, then read this site (the whole site AND links provided in it):
and you will have a fair idea of EFi/UEFI booting.