Besides the specs you've listed and the shape of the wheel itself, offset
is the key determining factor of whether the wheel will clear the brake caliper and other suspension components, or whether you'd need spacers. In this case, the G35 wheels have different offsets from the EX35 wheels (I assume you are referring to the 18" EX wheels since you mentioned the tire size as 225/55-18, and not the 17"). The G35 offsets are 30mm (at least the fronts are), while the 18" EX35 wheels have a 45mm offset. What this means is that the G35 wheels will sit further away from the wheel hub by 15mm, and stick out a bit more than the EX wheels. Not necessarily a bad thing looks and performance-wise, though it adds a slight bit more stress on the wheel bearings since the wheels are farther outboard (how much added stress is hard to say). Most aftermarket options for the EX seem to stick with around 35-38mm of offset (at least from a quick search on Tire Rack).
You can visualize all of this on https://tiresize.com/wheel-offset-calculator/
The diameter difference between 225/50-17 and 225/55-18 is about an inch (~4%) so the speedo error won't be too bad, but it will be about 3mph as you get towards highway speeds.