How much chalk or gypsum to experiment with?

I know there are people out there who do this. So I'll ask the question.

If I know I have very soft water (low hardness, but high initial pH) and efforts to brew brown ales come out tasting a bit harsh or acidic, how much either chalk or gypsum would I add to a 5 gallon batch to start to increase the hardness?

No, I don't have a useful water report. We had a massive flood with Irene and the local water supply is all fubar at the moment.

I also want the hops to shine through a bit more. Anyway, if I was to experiment, how much of either chalk or gypsum would you start adding?

I don't think adding chalk or gypsum would make the beer less harsh. Are you checking your mash pH?

I use 5.2 buffer. That helped a lot once I started using it to tame the acrid taste. But I understand that it does nothing to improve hop 'brightness' or character. So I was wondering if adding some chalk or gypsum wouldn't be useful to both balance hte mash pH and improve the hop chracter.

I would recommend reading this:
http://www.homebrewersassociation.org/forum/index.php?topic=1125.0

In a nutshell, 5.2 adds about 100ppm of sodium, and doesn't really buffer the way it claims to.

It is not a substitute for measuring and properly adjusting your mash pH.

Also, chalk doesn't really dissolve well in the mash. You're better off using slaked lime if you need to increase the pH, but I would never increase the pH unless you're positive, through measurement, that the mash pH is actually too low.