The Foresight rune on DR gives +18% damage on all attacks after the 3rd DR strike. My question is, does the DR strike have to actually hit a target, or can I (for example) shift-click while in town to attack the air, then portal out with the bonus?
You need to hit a monster to get the buff. You actually need to only hit the 3rd strike of the combo on the monster. I run with FoT[TC] + DR[Foresight] and Combination Strike passive. Easiest is to start with 2 hits of FoT (+8%) and then hit the DR button for the 3rd strike (+8% +18%), you get all 34% extra dmg from first 3 strikes. Then you hit sweeping wind and only need to use one of the spirit generators within 3 seconds from last strike to keep the 16% buff from combination strike of both spirit generators.
you need to hit something in order to generate spirit. if you go for the combination strike build you need to hit 1 time with DR for the 8% bonus, 2 more times with DR for the 18% bonus and then continue with thunderclap for the extra 8%.
so it's 1 thunderclap + 1 deadly reach for a combined 16% combination strike buff and 3 deadly reach for the 18% foresight buff.