Sorry for the slow reply, i do not swing by the game room alot. But i am willing to offer help.
the advice i will give you will be from the point of view that you have no one leveled up apart from the heros etc. And its been a couple of months since i played it so forgive me if i get confusing.
First things first. The second the level starts get you horses to go get the treasure inside the front door(on the left under the walkway, then go get the cash at the very edge of the deep on the inside wall…far left. As they do this build a archery tower on the base spot next to your heroes(left hand side) and build a armory on the right hand side. This gets you quick cash and you will build all your archers from this building so it will level up quickly so it will provide good cover fire later on, Build farms in every spot as quickly as possible, you need to store cash quickly before the deep is breached.
Send the horses down to the very bottom of the map and defend the refugees and they will give you more money, use your health spell to repair the unit for the next wave,
As you do this you must build archers as fast as you can, and build armour and unit upgrades, and then fire arrows.
Take each hero and space them out on the wall so they give extra upgrades to close soldiers, aragorn on the far left to protect your archers, legolas in the middle for the range and to take out the bombs, gimli and borimir on the right.
load every archer you have along the wall with fire arrows and unit upgrades(extra range and unit regenerate)
move the peasents to the center on the map, and let them get slaughtered(they take up unit counts)
the first wave will attack just as you are getting ready for it, close the upper far right gate do not waste any guards…they wont attack there. put to squads on each side of the main gate with fire arrows, they can hold the gate forever(or until your wall blows).
allows your horses to die and max out your unit counts with archers, when the attacks are coming hard, focus on scattering your archers along the inner wall overlooking the main gate, they are out of effective range of the crossbows.
When it is getting to thick and bloody on the main wall pull out the heros and start to shift your archers back towards the inside deep.
they will blow the wall, destroy your farms, so either close the armory and build a farm, or be ready to fight to the death with what you have,
When your archers are on the inner wall and leveled up(its a slaughter at the wall so they will all level up nicely) rain arrows onto the attacks from relative safety and wait, send your heros into the fray to level up but ensure they dont die as you wont have the money to bring them back from this point on.
When gandalf etc turn up its easy.
you do have some quite annoying levels to come, but its a awesome game, hope this helps.