Regarding the “lights”. They have their origin in paganism (avoda zara), which in turn looks to be a distortion of something done by Adam Harishon as stated in the Midrash. The Midrash states that after his cheit, Adam Harishon noticed that the days progressively got shorter and shorter (less sunlight every day). The shortest day of the year, is December 21 on the non jewish calendar. Within 2-3 days it became obvious that the days were getting longer again, and Adam realized that the lack of sun was part of the Briah (the seasons) and not something that was caused by his cheit. He brought korbanos on this day. With time, the world became steeped in Avoda Zara and this became a pagan holiday. When the Notzrim founded their religion it was very conveneient to use December 25th, because it was already a day the pagans celebrated. Part of “service” was to light lights to offset the lack of sun. Certain elements of this paganism remained with the Notzrim. Today, I doubt many associate the lights that are put out with the original Avoda Zara. I’m not a posek and am not issuing a Psak. just stating what is common in numerous books on history and religion.
Regarding saying “X-Mas” or its full spelling. Again, I am not a Rav, and am not stating a definitive halacha. Personally, I have a difficult time repeating the name that has been used as an excuse to kill yidden for more than 2000 years. The lights that celebrate this holiday and this persons birth/death (whatever) are also a vivid reminder of the jewish blood shed in this persons name. It bothers me to look at these lights, the way it bothers some people to buy a Volvo.
Again, not halacha, just how I feel.