Gypsum in the boil?

I'm using some store-bought spring water for which I have the complete water analysis. Unadjusted it has the correct RA for the beer I want to brew next, but it is low in sulfate. I'd like to up the sulfates to bring out the hop bitterness, but if I add gypsum into the mash, the RA goes down and I would need to add some chalk to get it back in range. Instead of doing this can I just add the gypsum addition to the boil and skip the chalk addition? I'd like to make as few mineral adjustments as possible.

Yes, I think you have the right idea. Since your RA is fine, and unless your mash water is calcium deficient (<50 ppm), then it sounds like you don't need to make any mineral additions to the mash, just adjust the sulfate level in the kettle.

Right, once your mash is good to go, flavor/balance additions go in the boil.

Thanks. What is the calcium needed for in the mash? The baseline Ca level is 43ppm - close enough to 50?

As long as you have been getting decent efficiency in your mash, I wouldn't worry too much. Palmer states 50-150 ppm is your target range. Calcium is important for many aspects of the process -- enzymatic conversion, yeast health, flocculation, etc. I am no expert, but i think 43 ppm should get it done. I have seen no differences in conversion efficiency using anywhere between 45 and 200 ppm in my brews, though I did have problems when I used to brew with only ~20 ppm, before I understood water adjustment.