That’s a good fare in premium economy. There are many people who speak English (and many who don’t); for conversational English and especially in touristy areas, you should be fine.
You could spend 3 days in Madrid and do a day trip to Toledo (highly recommend) and another to Segovia or El Escorial. Even Valencia is only 1 hour, 15-20 minutes on high speed train but I’d stay overnight if going there as there’s much to do. You could also consider splitting trip and going to Barcelona or Sevilla as examples. Both are 2 1/2 hours or a bit more depending which train via high-speed train. Focusing on Madrid with a day trip or two would allow a more leisurely stay.