Nice rims by the way! I am thinking the something similar for my Fabia.
The 215/35 R18's will be fine, but yeah as the others said just make sure they're 87 load rated.
Diesel_vert is getting down to the nitty gritty of the tyres, when they're talking about the 87V XL & 84V XL, which is what your tyre supplier should have done for you!
If you want to read about it it can be found here:
Tire code - Wikipedia, the free encyclopedia
The 87 and 84 is the loading index for each tyre. The V is the speed rating. The XL would just mean extra loading ie if the tyre had this marking on it, it essentially means it can handle extra loading.
So, the:
87V XL translates to 87=545kg V=240kmh XL=extra load
84V XL translates to 84=500kg V=240kmh XL=Extra Load
Also here are some good rim and tyre calculators:
tyre calc: Tire size calculator
rim and tyre: Custom rims, wheel tire packages for your ride - RIMSnTIRES.com
Tire Size Calculator - Tire & Wheel Plus Sizing
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