low profile has a height of 2.00 while high profile has a height of 2.06. it is dependent on the upper reciever which should tell you the size needed
Most likely not, the only options on this page that may work are listed under AR10. You will need to know if your Bushmaster is a DPMS High or DPMS Low pattern, and keep in mind both options are for 17.5" handguards.
https://www.opticsplanet.com/odin-works-o2-lite-forend.html?_iv_gun-model=ar10
Yes they come with the barrel nut for the model (AR15, DPMS High, or DPMS Low) selected.
Yes, it includes a barrel nut.