Heinie Slant Pro sights, straight eights if you want night sights. I have them on my G17, also had them on my Para P16 and G19.
3.5 pound connector. I haven't tested one that didn't make a 5 pound trigger pull. Mine consistently breaks around five pound three ounces on a lyman digital trigger tester.
Extra mags.
CR Speed belt, ghost holster & CR Speed mag pouches.
I've no experience with the Guga Ribas mag pouches but they look good.
The CR Speed holster is good, the ghost seems a little bit smoother.
No need to change anything else, if you plan to shoot IPSC Production Division you can't apart from adding grip tape or an A-Grip.