Most SB owners, when planning to use a wide, large diameter wheel, will use a narrow strut like the MaXX strut from
www.toplineparts.com, or a coil-over like the one that Kerscher makes. I can speak for the MaXX struts, as I have them on my Super. They have an 80mm diameter spring to allow large, wide wheels to be used on the Super Beetle while using stock steel fenders. I run a 17x7 et55 front wheels with a 205-40-17 tires, lowered 2.5". This is all under the stock steel fender. I also use a 3/8" spacer to help clear the spring.
If you wanted to keep the stock spring and strut combo, you may want to use a 16x6" wheel in the front and try to figure out the proper offset.
In the rear, a 7" wide wheel would be the best compromise between width and difficulty/ease of fitting. However, you can run wider wheels if you wanted to use a wider rear fender. I run a 17x8.5" et50 wheel with a 245-45-17 tire under a 1 1/4" wider rear fender and a 1" spacer. I had to cut the bump stop "perch" as well as replace one of the spring plate bolts with a "button head" bolt to clear the wheel and tire.
I hope this helps.