How to costomize starting document

Will the new document always have the same fixed width/depth in pixels?

Or will the size vary?

Does the perspective grid need to be at the original fixed aspect ratio of the original, or will it resize to the document canvas?

What is the original perspective grid - raster or vector?

What about the artboards?

If you save your document as a .psd then add a "t" to the end it becomes a .psdt file (Photoshop Template). You can then double click to open a new untitled document each time.