I just wanted to confirm, should I still be inputting the material properties and load magnitudes in the specified metric units?
Yes, you should do this.
How do the Peregrine components handle geometry that is input in inches, but loads and material properties in metric units?
If you hover over an input/output for any Peregrine component, a tooltip description will pop up, which will include the units of values expected by it. See the image below. For the majority of these, metric units are used. In some cases, such as the volume of a solution, you will see “using document unit”, so if you are working in inches, this volume will be in cubic inches. Non Peregrine components, for example those you might use to construct a mesh for your design domain, are generally in document units. I’ve noticed that the units are missing from the tooltip of the volume outputs of a few components, as well as from the minimum area input of the line structure and surface structure components, so please note that all volumes and areas are in document units. We’ll address this in the next update.
Would it be easier to keep all files in metric units, and just convert my geometry to metric units?
I would recommend doing so. You could also use the Grasshopper multiplication component to convert units you are more familiar with into metric units to be used as inputs for components, although I appreciate this introduces an extra stage, and isn’t possible for the material properties. I will raise this matter with the development team; it’s possible we could implement a more elegant solution in a future release.