Generally speaking, if your wire looms aren't touching anything, you're probably OK. In the direct area of a high heat source though, like the headers for example, I would try to keep the wiring as far away as possible. For my Coyote builds, for the sensor and alternator wires near the headers, I routed them away from the headers as best I could and wrapped with this tape from DEI. https://www.summitracing.com/parts/dei-010408.

Yea, get those ignition switch wire terminals covered. Kind of a worse case scenario there. You're dealing with direct battery power plus it's not fused at that point. So touching to ground is going to start some serious action.

On the Roadsters, we've found the location of the GPS antenna isn't super critical. Many of us put it on the windshield mount (it's steel, so the magnet holds very well) that's in the corner of the dash area in front of the windshield. It's under the fiberglass body, but doesn't seem to have any problem acquiring and keeping the signal. I've had mine there for two seasons of driving. Long answer to say I haven't found the final location for mine on the Coupe build. But will probably be also somewhere under the body. Just not shielded by metal. David W's suggestion is one I've also considered.