1) The Dacians didn't have walls like in RTW. Made of cut stone, five stories tall, smooth, and straight. Plus, I'm under the impression that, yes they had stone walls and road in AD115, but didn't in 272BC.

2)

3) Yes, little is left of Dacian language. I'll be corrected if I'm wrong and I'm not sure of this, but I remember hearing that the Getai tribe (but not other 'Dacians') had adopted a form of Greek.