what would i need to add to topsoil in a raised bed if i wanted to grow...
Compost, Leaf-Gro or other organic amendments are beneficial. If you were starting from scratch with a raised bed, we'd suggest a 70/30% mix of top soil to compost.
The proper pH for growing potatoes is 5.0 to 6.5.
The only way to really know with certainty what your pH is is professional soil testing.
Here is our page on soil testing, including linked chart of labs which can complete the analysis for you: http://www.extension.umd.edu/hgic/soils/soil-testing
Please take a look at the vegetable portion of our website called Grow It Eat It, to see much more information, including vegetable profiles: