I was super reluctant to get a full GTS package (1.7k + 3k eur), but when I sat in base leather interior I decided that the upgrade is worth the money. Base interior (no leather) looks like crap and is only worth it if it's a track focused car and you're saving money and weight. Base leather interior is better and has a premium feel, but aluminum detailings are a bit bland, and once you start adding more stuff, you might as well go for GTS interior, which is a good value.
Secondly, black calipers will look amazing on your color and wheel combo. I personally have black wheels + red calipers and went for red GTS interior to balance that out, but you have a more classy look, so I'd consider a GTS interior in chalk.
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If you drop bucket seats, then definitely get 18-way adjustable Sport Plus seats. They are amazing. And depending on your area consider getting heated or ventilated seats (or both).
A minor detail but consider getting 718 logo on the back in black. Will look better than chrome on arctic grey. Just a humble opinion.
Edit: if you have a manual transmission, then 18-way seats are not a must-have, so you might consider saving money on them. Ideally try both, or just go for 18-way if money is no object. But definitely get Sports Plus.