Yes, + offset sits closer to the center of the car; - sits further out. 0 on a 7" rim is probably pushing it... especially up front. I think your fenders are going to be over the rubber.... one big bump while turning and you may suck your fender into the well. On the stock 4x4 suspension you're probably ok, but if you lower it, well... Someone did it on SM, might see if you can find the thread there and the beautiful body job; I think he posted what he was running.
If he's your friend, then why not just try them out? You need to make sure you have the right size center bore or that they're built to accept hub spacers too; The MKIII relies on hub-centric fitment for proper balance.
8" wide with 12mm offset is pretty much the same as the 7" with 0mm offset as far as clearance... You're moving the wheel 12mm in, but you're adding almost that much right back.
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