I agree with the others who say that after Findan handles the initial counterattacks on the first couple of days, hire a rookie hero to defend, and let Findan move on. I gave Findan the Dragons, Hunters, and half the Druids. For Findan and the defending Hero, split the druids into equal stacks to fill in all 7 slots, for more lightning and stone spike joy.
As you get minerals to do so, make upgrading your defensive troops the top priority, so that your new recruits will stack with the troops you already have to defend. Don't even bother to recruit anything except druids until they are upgraded (except maybe Dragons). It is better to have an extra slot for splitting druids than to have 14 regular unicorns and 50 silver unicorns. So just don't recruit them until you can get silver. Same for the others.
Findan should blitz through the area. He can take the first mainland city on day one, hire a hero to follow behind him picking up gold and minerals and such, so Findan does not have to slow down to do that. Findan had expert Logistics and Pathfinding; this really helps!
Your defensive hero has to handle one battle before you upgrade and buy much in the way of reinforcements. One defensive tip: have a stack of druids take out his ghosts with lightning or stone spikes, since magic never misses. This will free up your towers to fire at more worthwhile targets for future volleys. My defensive hero got a bunch of levels out of this. I got expert light and a couple of the mass abilities just from the levels gained from this one battle, which really helped with the next battle. By the time the next battle came, I had upgraded everything except dragons (including the +2 luck for defending heroes, don't forget this one), and had bought everything the castle had for reinforcements, so the battle was not too tough. Meanwhile, Findan blitzed through, releasing the first hero and grabbing some good artifacts, then taking out the two garrisons to get to the second hero. Done this way, the scenario is really not too hard.
I don't think I've ever played a worse heroes map. Have to defend main town against never ending waves of necro heroes.
Who in first week come daily, later a bit rarer, but expect one each week.
Those heroes have lousy stats, but are 20+ levels, and they don't waste much time on spells.
Most of the times attacking your dragons, treants, unicorns. Also, each hero has a bigger army than previous one.
And while you defend the town, you must get 10 green dragons, 30 silver unicorns, and 50 druid elders.
Plus you must find two heroes that are in prisons in the land.
And as for this being worst heroes map I've ever played, it's not just becuase of those necro waves, map is also pretty ugly, with lots of wasted space.
Anyway, first time, I defended with Findan for literally months.
No mines at all to build those dwelling that are needed, so only managed to trade and build in month 3, 4...don't know now.
And just when I got those troops needed for objective (one that says that with them, town will be able to defend itself), and finally went with Findan to attack teal, ofcourse another necro heroes came. Bleh.
Second time went well.
First day, retook town, left all the troops in it but master hunters and unicorns, bought a hero (was Ossir), and went with Findan in boat.
Findan went south east, to take the town that eye of the magi reveals. Ossir on the other hand leveled up quite fast.
No wonder with that many enemy.
Eventually he lost all emerald dragons, but at same time other troops (and green drags) increased in numbers.
Anyway, Findan cleared area, took mines where that other town is...and when you feel ready break that teal garrison.
Regular inferno army there 10 some spectrals, 15 or 20 wraiths, 30 or so archliches, and so on.
Actually there are two garrisons on same road. Also, teal hero might come out as well.
Findan with help from some troops from other Sylvan town managed to beat both garrisons, teal hero, and finally poorly defended necro town.
Now just to get those two heroes (and those troops previously mentioned - they have to be in garrison in main town, as soon as you remove them from there, objecitive is active again).
One hero is underground for which entrance is near necro town. Second is close to south-western corner guarded by some titans.
Those heroes will be active in final scenario of campaign, so up to you if you want to level them up a bit.
I did, just one, underground one...but as it turns, all I needed from her was ability to cast Summon Creatures.
So good knowledge would be plus.
And logs as well.