Instead of converting to a Shape Layer you could convert your Text to a Solid: Layer/Create/ Create Masks from Text.
On the solid you can apply a Stroke Effect which will use the Mask Path to draw you'r outline across. It has similar animation option to the Trim Path. For it just to create the outline and not the fill, set the Paint Style to 'On Transparent'.
If you do your first number, then you can either Copy the Effect with the keyframes or 'Save Animation Preset.' This will save the Stroke effect along with the animation so you can apply it to each letter / number you create.
You can even assign a Keyboard shortcut to 'Create Masks from Text' so you don't have to go through the menu every time:)