I poured the raw apple cider into a carboy and added crushed campden tablets to eliminate or knock down the native bacteria a couple days ago. Now as I am about to some S-04 yeast, I wonder if I should first rack it into another carboy so that I can remove the solids which have settled out. Does it matter?
It might matter, in two ways:
Some solids may, in the long run, introduce tastes you do not want. And getting rid of them may help with clarity in the future. Also, if your tablets are not completely dissolved yet, they may still release sodium metabisulfite that might not be exactly healthy for your yeast.
By decanting it to another carboy, you introduce chance for more oxidation, and for fresh bacteria from the air to contaminate your cider. This might ruin original purpose of adding these tablets at all, if you are not careful.
I don't believe there is one universal do or don't answer for this one. Consider possible benefits and risk, and choose what feels right. First few times it'll be guesstimates, later your experience, knowledge of your skill and your workshop will guide you.
I do not think it matters at this stage, you can rack it or not, as you wish.
Personally, I would not rack anything prior to fermentation. In all the books I read about beer or wine making, I have never seen anything about racking before any fermentation.
Some solids are beneficial in the early stage (adds to flavor and color in wines), so I would even stir everything (using a sanitized spoon) before pitching the yeast, it will also help to get rid of remaining sulfites.