Can the SN54LS47 BCD to 7-segment display driver sink current of a full 7 segment display
It's common to have several of these displays connected to the same driver and switching between the displays with the common anode; i.e. each of the A-G segments are bussed to the 7447 and a transistor is connected to the anodes of each display.  Relying on persistence of vision, the segments are quickly (~kHz) turned on one at a time, then the next, and so on.  This way fewer components are needed and the current required may be reduced, albeit with lower brightness.

A. tW probably means the period of these switching cycles.  At 200mA peak current, the switching period must be &lt;=1ms (i.e. f>=1kHz) at &lt;=10% duty means the current can be pulsed at 200mA for a maximum of 100us.

A. Potatoes, potatoes.  Physically it's outputing electrons, but yes, they're a bit inconsistent with terminology in this datasheet.

A. On page 9, under 'recommended operating conditions' it lists a maximum 40mA per segment ('On-state output current, IO(on)').  You'll be fine with 10mA per segment.

A. Active-low means that the desired output will present a low value -- here it's a ground signal to sink current.  If it were active high, such as with the CD4511 for common-cathode displays, the desired output would be a high value (+Vcc).