I'll try my best here...
First, good place to get acquainted with how it works:
zerothread/57950
Here's a good calculator (listed in the thread above, but the link is broken - fix?):
http://www.1010tires.com/WheelOffsetCalculator.asp
If you upgrade to an 8" wheel, you'll want to have an offset somewhere around 30. (That would push the outer edge of your wheel out 25mm or ~1".
...
I just spent the last hour combing the internet of options and unfortunately you're very limited because of your lug pattern. In order to get the wheels flush, you will need spacers.
Here's a half-a** chart of what you can do:
Width...............Offset..............Spacer Thickness7.........................42.........................20-25mm7.........................25..........................5-10mm7.5......................35.........................10-15mm8.........................35...........................0-5mm
I like these:
http://lsdmotorsports.com/prod/00377087.html (~$800)
^That with a 20mm spacer would have you sitting nice:
http://www.ichibausa.com/20albowhsp7.html (~$270)
or you can pick 'em up from this guy:http://www.northwestnissans.co...05712 (~$140)