A lot of people recommend a separate ext2 boot partition with around 100MB space for Linux installations. What is the significance of this separate boot partition.
Ok i think this is close to a myth specially that nowdays distros tend to update the kernels a lot during the stable cycle and not remove the old ones. Which means if you have 2 kernels (or even one) it will fill out 100MB including the grub installation and initrd. The real advice to do a /boot partition was because the bootloaders don't work well with some filesystems like xfs or btrfs.
Nowdays on modern Linux distros ext2, ext3 and ext4 are equally supported so it means you can use one of them. The use of the /boot partition makes sense if you want to use other filesystems besides ext* or you want to preserve your Kernel images between several root partitions (/). If you decide to use /boot partition i strongly advice to fill it with around 1GB.
This it debatable, it depends on the context.
On simple desktop installations or laptops it didn't make much sense the last years, in my opinion. It was easier to use just one system partition. On linux routers (using BIOS) I also don't use a separate boot partition.
If your system uses UEFI, then a separate boot partition is mandatory again (EFI system partition), but ext2 is not a good choice, I would recommend FAT.
A valid case is if you use a boot manager that cannot boot from your root file system then a separate boot partition makes sense and ext2 is most likely to be supported.