1. Battery life is excellent and from my experience, superior to the Lumia 920 and Galaxy S3. Just as with any device, playing games can drain the battery very quickly. Some games will take you from full charge to 20% within 1 to 2 hours. At this moment, my ATIV is sitting at 66% remaining charge after 18 hours including a few phone calls, texts, and app use.
2. I don't know, but I have friends who have these (ridiculous) giant battery packs on their Galaxy S3 and S4. It makes sense that there is probably one for ATIV S, but I'd say that you don't need it.
3. Fast enough for a solid user experience. No lag, no problems running any apps or games.
4. There is a micro sim slot. I personally have never used it.