if you can get your hand on the Jeppesen multi manual... it does a pretty good job. pretty much any multi engine training book can explain it. you wont really have to get to technical on your Comm multi checkride but they will ask you to for your mei. Your mei is one of the best ways to build multi time ... in jersey and new york there are quite a few multi students here and there. instructing part 61 is tougher but you can try and get into a part 141 school and there will be more instrument students and multi students... those are the best students to have as they keep your instrument skills sharp while keeping multi aerodynamics fresh in your mind. hope i was a little help.