If a large percentage of your fermentables come from extract, then the best thing you can do is to have as little mineralization in the water as possible. Brewing with a larger percentage of RO or distilled water is more likely to produce a good beer. If the local water has low mineralization, then its OK too.
Don't worry about the steeping or mini mash too much in this case. But as the mini mashes grow to mashes, then you need to think harder about your water.