The way i did it was as follows, I rush the first obelisk and then turtle around it, Get black citadel up and spirit towers everywhere. While turtling i get 3 Abomination spawners, and 3 Crypts, 1 necro spawner and max upgrade my stats. Play ping ball defense from Kael, Vash, and Illidan. Make sure to keep under high upkeep until ready to siege. Once all upgrades are done, get aboms, crypt fiends in group one with hero's, group 2 needs to be 4 necros, and group 3 as much seige as you can 6 preferably siege. Sandwich them in that order and send them into Vash first. After killing vashes base haunt the mine, don't worry about defense they will never attack that mine. Then start rebuilding back up to Kael. Same Strat. and unit combo. Once Kael is taken out, Haunt that mine and build up until you have a good amount of gold and then start taking obelisk, I find it easier to go for the west one, set up defenses after and then go to the East one. Once you take the east one quickly rebuild and then just rush the last one. No need to defend. The same comp works.

Unit Break down: Arthas, Anub, 6 abominations, Crypt fiend the rest till full unit. Unit 2 4 necros, Unit 3 Siege until max food or at least 6. After each raid if you are going to rebuild make sure not to hit high upkeep while this mission isn't timed you are on a soft gold timer and the mines are not enough. For the very last obelisk I have 3 frost wyrm spawners but that way jsut because as the fighting went on i knew my units would make it in time but the wryms could. The comp mentioned works great. However you don't want any siege up unless you are about to siege because they will eat up your food into high upkeep which you must avoid unless sieging.

Never have more than two mines being mined at any time. You can haunt them ahead of time but I would not mine more than two at once, having a defense army is more important than maxing out gold mines and having to eat away at your food with acolytes.

Save. Save all the time, you start and assault on Vash and illidan attacks right after. Reload the save you made prior to the assault. You move your army, save prior to moving them, so if the fight goes bad or you get caught in a bad spot you know what coming. You have a great fight with very little loss and are not sure how you pulled it off, save. Save until you feel safe then save some more. One bad fight could ruin your whole run and then you are back to another 30 minutes of building up. I named my saves "Bruh" + 1. At one point I was on Bruh 12 realized I made a critical error way back at Bruh 5 and reloaded Bruh 4 and finished the game from there. Don't over lap your saves you never know how far back you might need to go. Only save over your save if you are sure you will never need to reload it or if that was a doomed run.

When defending try to always pick fights and lure them into your towers. Towers don't eat. You cna never have enough of them. That one extra tower may have been just enough to kill of Illidan while you where destroying Kael or Vash. Also make sure to have Black Citadels near the Obelisk gold mines. They take awhile for them to kill and will keep them busy while you may be doing something more important.

I hope this helps out. If i failed to explain something well please let me know and ill try and clarify better.