I have an S4R and wanted to do a brake upgrade after riding a 999. I put the four pad calipers on and feel that I'm much closer to 999 performance braking than the stock S4R braking. Try the four pad calipers and that might be all you need. They were about $370 for the pair including shipping. You also need to change your front brake line when you do that. Other than that, it's a direct bolt-on installation. I sold my stock calipers for about $200, so it's a very cost effective upgrade. If you feel you need more performance than that, you can start playing around with different pads. The GP master is not as much of a performance upgrade as the four pad calipers.
I also installed the Surflex slipper on my bike. It was easy, except that you'll need a 19mm allen for installation. I couldn't find one locally, so I made one using a bolt with a 19mm head. The Surfles slipper works great. You still have to be careful when downshifting in delicate situations, but it makes it a lot easier.
Unless you ride like Rossi the majority of the time, I don't think that Ohlins is a justafiable for the S4R. My last bike was a monster S4 and the stock rear shock was Sachs and it was junk. I put an Ohlins shock on the back and it was a great improvement. The S4R comes with Showa pieces front and rear, and are not garbage. Make sure the springs are good for your weight and set up correctly. For the street, Ohlins only raises the bling factor on the S4R.