Do touchstone (s2p) files for capacitors from include the ESR/ESL, or do I need to add an ideal R/L for simulation?
Yes the vendor supplied S2P file will contain the effects of ESR and ESL. The model used will be somewhat more complicated than just a simple RLC combination, accounting for current crowding in certain parts of the capacitor structure as frequency increases.
If they didn't include these effects (i.e. if they just modeled an ideal capacitor of a given value) there wouldn't be much point to having the vendor supply the S2P file instead of just using an ideal capacitor in your circuit model.