Luster is a result of mechanical stress of steel under fore of repeated impact. At it's beginning, and die has little or no luster because its surface has been formed to match that of the hub. Acid dipping contributes to averaging of the metal surface. Under repeated high pressure impacts die steel gradually deforms into a radial pattern (based on planchet metal flow from center to periphery). This is stable for most of the die's coinage life, but eventually the ridges begin to break down and steel particles rapidly etch the die surface. At the beginning of this breakdown, the die should be pulled and condemned.
This is completely consistent with what I've seen in documents, especially the Royal Mint in the 1880s, and first hand examination of dies.
No. The force used was similar during the Liberty designs and decreased a little with Saint-Gaudens and Pratt designs. Silver dollar-size coins required the Mints largest presses. A bigger press was desirable for DE because it put less stress on the machine, not the dies.