Yes the effects are cumulative, you can combine all effects at the same time if you wish (and
TBH, you will use them most of the time).
Yes.. if you have high level
MA you are bad-ass
Regarding your first final question, you have to state your intended moves at the start with the unit. Also with
ARO - for example you see a camo token coming towards you, you can choose to hold back the
ARO for if the unit reveals (and then shoot). However, if the unit remains as a camo token (and doesn't reveal to shoot for instance) the order is wasted.
Basically I guess it indicates the soldiers know something is there, and are watching like hawks waiting for an attack to come their way so they can return fire, as opposed to using their scanners/taking a closer look (as represented by the 'discover' order).