Do you call "At ease " or "Attention" if your alone?

I did. A room with 1 person or a room with 100 is still a room with rank walking in. Might they tell ya to knock it off? Maybe, but that doesn't mean you were wrong. Besides, better safe than oh-so sorry.

Silly question for the group. If I as a CW2 am in the same area where other Soldiers (CPT's & LT's as well) are and a CSM walks in, is it appropriate to call at ease?

Always go "by the book" the first time, and then let your chain of command set the climate with you afterwards.

No

Highly recommend it! They like it! Shows respect.

Attention is for officers (c/o)

No. But you snap to parade rest.

It became 2nd nature to just say that!

In my day hell yes!!! Two reasons one keep Top or the CSM happy, but the most important reason was to make sure everyone know they are on the floor.

Yes, I do. Heaven forbid, I even do it for, shhhhhh, officers.