Needs a MicroSD card for the Pi 3. Doesn’t need to be too big, 8GB should be enough for the basic OS. But 16GB or 32GB are cheap enough anyway.
For software, Raspbian is easy enough to download and install on the card.
Screen – it has HDMI out, so you can plug it into any modern monitor, or TV. You will need an HDMI cable (Poundland usually sell them).
Yes, it can be powered from a phone charger. Though worth getting a decent one, that provides enough current. The Pi could use up to 2A if you have a few accessories attached.
Camera – depends on what you want to do. Most USB webcams will probably work.