I will try to answer some of your questions in a non-partisan way.
Pegasos is the name given to a line of PPC computers. Most run MorphOS.
AmigaOne is the name given to another line of PPC computers. Most run AmigaOS 4.0 or AmigaOS 4.1.
AmigaOS 4.0 is also available for classic Amiga A3000, A4000 and A1200, however you must have a PPC accelerator card.
AmigaOS 4.1 is now available for AmigaOne, SAM440ep and Pegasos II.
I am not very familiar with AROS. As I understand it, they were trying to make it run on a variety of hardware, including x86 PC, SAM440ep and some others.
There are many products which allow a PC to emulate AmigaOS. One is WinUAE.
redfox