I am looking to get some steel wheels (diamond racing steel wheels) and would like to order 13x7 w/ 0 offset or more -offset. The 1980 datsun 210 hatch i have has rolled fenders in back with non rolled fronts. What is the lowest offset 13x7 i could get to fit on my car? BTW tires are 185/60/13 toyo R888's and car will be on short stroke coilover suspension (front) cut spring/AGX shock (rear) PLEASE PEOPLE HELP ME OUT.

A HUGE limiting factor in your situation is the tyres you want to run. I suggest getting some smaller tyres for them. As for the offset, you can fit -10 under B110 front gaurds pretty easy if you use the right tyres and get rid of the factory positive camber. The B310 (210) has much bigger gaurds so you should be able to swallow that up pretty easily.
Fit a wheel and do some measurements to get the best information

Like 50 series or 175's? are the 185/60/13's too wide and i need to have it stretched over the rim more to clear the fenders? or less sidewall? 185/60/13 is just the right amount of tire around 7" wide wheels. Please Elaborate

I used to run 205/60x13's on 13x6.5 inch wheels on the front of a 210 (b310) & they were well outside the guards. I have also had 195/60x14's on 6x14's & they were in the guards. So the 13x7's with 185/60's will probably be outside the guards. If you get the guards rolled, this might be enough to cover the tyre. All you can really do is measure from the hub face & such, & talk to the people selling the wheels.