Does Apple Watch navigation require carrying an iPhone?

No. After the route is transferred from the iPhone app, the Apple Watch stores the route and offline maps locally and uses its own GPS throughout the activity. The iPhone can be left behind.

Is TouchTrails free to use?

TouchTrails is free to download. Route planning, GPX import and editing, and 3D route imagery are available without a subscription. Premium adds GPX export, offline maps, turn-by-turn navigation on iPhone, and standalone Apple Watch navigation.