The templates shipped and installed with Rhino are for convenience and are nothing special. The templates labeled “Large” have an absolute tolerance of 0.01 and 500 grid lines. The templates labeled “Small” have an absolute tolerance of 0.001 and 200 grid lines.
The absolute tolerance should be at least one order of magnitude smaller than the minimum size of details being modeled and the smallest manufacturing accuracy. An absolute tolerance tighter than needed is likely to result in more control points than needed with various operations.
The grid settings can be what ever the user prefers. The grid is just a modeling aid and has no effect on the geometry, other than providing a method to locate points if Grid Snap is on. Usualy it is preferable to model with Grid Snap off unless there is a specific need to snap to the grid. Many users like to model without a visible grid.
Any file can be saved as a template file using SaveAsTemplate. It will then be available for selection when a new file is started.