tbh the double arms and the new face dont really add anything to the character, if anything they detract from it. those legs are ****ing pwn though
just creating an image of what he would look in my head, it looks much more stylized with only the top arms. also if you gave him somewhat of an arched back afterwards it may help give him back some of the insect-like appearance. (like the giant bugs in re4)
the face also, if your trying to do your own version of him thats fine, its just that the face itself doesnt really "scream" imperfect cell like the rest of it does, I dunno if its too late to say it, (seeing as you already skinned it) i think it would also help add to the character if you made his face a little closer to the original imperfect cell. at least to inject some of his original "character" back into the model.
oh and the current versin of esf would support that model just as well as 1.3 would, unless im missing something anyways.
1.3 just has the option to swap between original and custom models ingame, (again, unless im missing something)
if you really did want to throw him ingame, you would have to either edit the existing skeleton (alot) or make a whole new one from scratch, (i think your only problem would be bone names for animation blending) and remake every single animation as well