I think the first question is which version are you thinking of getting?
As Neil says the front tower is as vunerable as any other car, I remember marshalling at a regional a couple of years back where all the cars in the heat where XX4s except one Lazer and one B44 .... at the end of the heat the only car still circulating was the ZX5 ... all the Losi were sporting the latest 2 piece shock towers
The cars have all been open the box, build and race (except possibly the original ZX5 which did require options to work in the UK). Other than getting some springs to tune the car with (happy to advise when I know which version) I'd say run it as it comes and see what you want from the car. Once we know that, what setup you ran and the model version there are several of us here who would be only too happy to help you tune it in to suit you.
That is the major strength of the Kyosho brand, they can be tuned to suit anybody easily, yes you may need an option part to do that but on the whole they are a one box race car!
As far as cells are concerned if it's on the BRCA list it will go in! I am hoping to get my hands on some Orion packs in the next couple of weeks but haven't found anything (on the BRCA list) that I couldn't get in with anything more radical than a spacer under the posts!
Diffs and slipper .... LOOSE .... far looser than you would any other car. Does it feel wrong to build them like that, yes, does it work on the track hell yeah! Again several of us would be able to advise there but njc11 (Nick 'The Diff' Caro) is the main man
Have you got it yet? What are you waiting for!?!?!