Consistency? Not at all :P Even different traditions have their different "traditional" altar set ups. It's interesting, really! The two above don't look like the altar layout in the tradition I'm in, for example. A lot of people don't go for all the "frills" either, when it comes to tools. I did, because I really enjoy it. Also, it depends on where the altar is facing. Typically most traditions agree that it is usually facing North or East. But the last place I lived in, the best place to put the thing was where it faced South. So I moved all the places of my tools, so they would correspond with the directions. So I think customizable would be the best idea

I'm not sure about picking some standard sizes for the actual cloth either. People use different surfaces. My main one is an old coffee table (that I had my husband chop of some of the legs so I can sit on the floor). My deity altar is a foldable side table I got from Target that is probably the height of a card table but not as big. I've seen others use chess tables, board game tables, tops of dressers, shelves, etc. And all of those are different sizes- some are square and some are rectangular. My guess would be to make them bigger so it will cover the table (if it's bigger or smaller) then the excess can hang down off of it.

As far as material goes, I've leaned that silky things slide around and bunch up. Even if I straighten it all out and just leave it, I'll come back and it will have bunched a bit (and it's more noticeable since the material is shiny). Just something to keep in mind. Can't wait to see what you make!