No, the 180 and 7.2v will not fry the esc. As for the NiCad holder...yes...it screws into the chasis where the other single cell holder is. One thing to be careful about though. You have to make sure that the dimensions of the 7.2v pack will fit inside this holder that you pointed out. There are several and probably dozens of battery packs. there are even some that will fit snuggly into the compartment once you take out the single cell holder. my advice to you, since i am not much on the battery specs and whatnot, is to go to some of the other threads about battery packs. poke around, there's tons of them.
and the dynamite mini mod motor....not too sure on that one. I'm certain that it is at least quicker than the stock motor. I actually put the elite micro stock motor in my second rocket racer.
http://www.hobbypeople.net/gallery/854841.asp Very cheap and very effective. I would say this is plenty of power for the first upgrade. Then once you get the battery pack in there, youll really be screaming! Same motor that would come stock in the Micro RS4 i believe. and that sucker really gets up and goes. major difference from the dynamite stock motor.
hope this is not too long winded and that it helps.