Line patterns are part of a line style's definition (otherwise all line styles would be use a Solid (or 'Continuous') line pattern. Therefore if you were to ask the chicken or egg question (i.e. "which needs to be created first?"), it must be the line pattern.
You could have these all created in a single file, and for a single office this might be deemed a better way of doing it, but for ultimate flexibility, I think that to keep such files separate is better. Also, you can build into the files some samples to print, which can be useful in documenting your standards. You can have a sheet showing line PATTERNS only (no pen thicknesses and no colours). You can have another sheet from the Line Styles project file showing samples of all your line STYLES which incorporate these same line patterns, as well as colours and pen thicknesses.
It's a hierarchical approach, I suppose - just based on what has to be created first, and working your way up the chain until you get to your template and/or project files.
Hope this helps. Let me know if you need more info.