Hi fildil
Boy been awhile on this one. If memory serves there are 7 imps to start with - but two or three are used on "suicide" missions.
I didn't know this at the time I played the game but when you use all your imps - they regenerate in their same location so technically I guess you could say you have unlimited imps.
And as I recall there are only three save game slots so you have to over write your imps