to answer your points
airlines wouldn't give a hoot whether you did a single IR first or not. all they want is that you hold a current multi IR.
if you got a MEP rating this does NOT give you multi IR privileges. you need to sit a 15 hour course to add multi engine to a single engine IR.
having a SE IR will help with your ME IR. however, the two are not really that similar with the hardest part being all the single engine asymetric (sp?) work.
if i was you, i would bite the bullet and get the ME IR initally. works out cheaper and gives you the SE IR privileges as well