Regular is a starting point
Begin with a well-proportioned Regular master. Its line width, counter space, and margins establish the decisions that the other weights need to preserve.
Use automatic weights as a first pass
SymbolBuilder can create all nine weight masters from Regular artwork and Auto-Suggest a line width based on the proportions Apple uses. That saves the repetitive setup work; it does not remove the need to look at the results.
Review optical balance
At lighter weights, strokes can disappear before the outline technically becomes too thin. At heavier weights, counters and tight corners can close up. Check the symbol at small interface sizes, not only in a large editor canvas.
Keep the family coherent
The point is not to make nine unrelated drawings. Each master should feel like the same object, with a consistent centre, silhouette, and visual rhythm. Use the live preview to compare the whole range before export.