The only "dress code" DCL has is "no swimwear in the main dining rooms at dinner, please" (well, except for Remy/Palo, they have a higher level of dress required). Beyond that, you'll see all manner of dress at dinner, from cutoffs/t-shirts to full formal wear. Do what works for you.
You can have the request to be seated alone added to your reservation, but it's not guaranteed. At late seating it seems to be more often granted. Or, if you book Concierge, the default is to have a separate table for only your party.