Dual boot Windows10 and KALI LINUX 2018.3a boot issues.

Hi there! I?ve been trying to install the latest version of kali linux i.e 2018.3a and dual boot my system wherein Original version of Windows 10 is installed. The problem I?ve faced is that even though the installation was successfully finished, after restart windows 10 booted up . Even I turned off my SECURE BOOT and FAST BOOT from bios , after installation when I tried opening Debian/ GNU Linux , error is displayed ?/g2ldr.mbr? .
1. In the process ? Install Grub Boot Loader to Master Boot Record ? , I selected No, thinking I may never be able to boot into windows again, as the warning says : This will lead to not accessing your other installed Operating System.

2. I created different partition from where I ?manually? installed grub boot loader into /boot partition.

3. Later after Installation, when I installed EaseBSD application to manually add linux boot, message displayed was- ?It was detected that you are using EFI boot hence as Microsoft has some security protocols?, and in the EaseBSD application there was already Windows 10 ( default) and DEBIAN/GNU Linux.

Also before all that when I changed my boot mode from UEFI to Legacy Windows 10 wasnt being booted and kali from pendrive was booting up.

My 3 Major questions are-
1. Should I use Legacy boot Mode ( under it has options : UEFI or LEGACY ).
Is there a risk factor or chance of losing Windows in this case?

2.Should I Install Grub Boot Loader in Master Boot Record?
Is there a risk ? Or will cause damage to normal system? Like not being able go access windows at all?:(

3. Which partition method should I use-
/boot , /swap, /home, / OR Automatically partition the drive?