Warcraft 3 Frozen Throne Walkthrough for Night Elf Sentinels:
Chapter 7: The Ruins of Dalaran
Main Quest: Spell of Destruction
When you first start, train five wisps from your Tree of Ages. Hotkey Malfurion and Maiev and send them to the northeast to rescue the paladin. The two heroes are quite powerful enough to take care of these few battles. The rest of your units should be set to guard your base for now. Hotkey them into their own separate group.
On the way to the Paladin, you can find a Kobold taskmaster that drops a helm of valor (+4 strength/agility). If Maiev still has the robe of the magi, give it to Malfurion Stormrage and take the helm for Maiev. A second group of Kobolds will drop a tome of intellect for Malfurion. During these battles be sure to set your wisps to gather wood from the trees, and research tree of eternity as soon as it is possible. Save one wisp to do your building. Once you reach the paladin, add him to your hero group and return to your base. Buy an orb of venom for him from your ancient of wonders so that he can have a ranged attack vs. air. If Maiev has the shadow orb then all three of your heroes can hit air.
You need to spend more time at no upkeep. Use this time to research upgrades for your units. Only take the following: everything at hunter's hall, moon glaive upgrades for sentinels and durability upgrades for mountain giants. Make a chimaera roost and upgrade their acid breath once you reach 100 max population cap. Send that idle wisp to grab more lumber at this point. I found several units to be throwaway: (only for this mission, don't flame me!) druids of the talon, fairy dragons, archers, and druids of the claw. Send them all to their deaths into the enemy base. This will free up food cap for you so that you can build more units. This should put you at 32/100 once you have all moon wells built by your lone worker wisp.
Army composition should look like this in the end:
The actual push toward the summoners should go like this for 3-4 fights.