Help me please

[Drift_Office!]

I have a 93 isuzu pickup with a 302 and a 4 speed swap. I want to lower the rear by 5" and the front by 4". I would also like to put 15x8" wheels up front and 15x10" wheels out back. my problem is i am having trouble understanding the whole offsett/backspacing thing. from what i am gathering i need a 0 offset, but im not sure if that also applies to the rears as they are wider than the fronts. ANY help would be greatly appreciated. ive checked out the calculators and the information but for some reason i just cant finger it out.

[RX N8]

What kind of fitment are you going for? Flush or poke? Pictures are helpful so post fitment goals if you got them.