Short answers, pulled from the story.
Trajan launched his first offensive into Dacia in 101 CE after receiving Senate approval. Roman forces marched directly toward the heart of enemy territory and defeated a major Dacian army at the Third Battle of Tapae.
Decebalus committed suicide rather than face capture by his enemies after fleeing from the fallen capital Sarmizegetusa. Romans found his hidden treasure thanks to treason from a confidant named Bicilis near the river of Sargesia.
Carcopino estimated that the fortune contained 165,500 kg of gold and 330,000 kg of silver recovered from the Dacian treasury. This wealth contributed significantly to the Roman economy following the conclusion of the wars.
Apollodorus of Damascus designed both the pontoon bridge used in 101 CE and the massive stone bridge later constructed at Drobeta. This structure remained one of the largest bridges ever built and enabled rapid troop movement into Dacia.
The Roman Empire signed a treaty with King Decebalus of Dacia in 89 AD which included an annual subsidy of 8 million sesterces and provided craftsmen to help build Roman defenses. Instead of securing peace, Decebalus used these resources to fortify his own kingdom against Rome.