Alright, let's get to work...
Starting with heroes, make use of Beregond, Faramir, and Denethor at small game levels- they give you enough heroes to put a decent number of models on the table (which Minas Tirith needs) while also giving you some fighting power (Faramir and Denethor). In larger games make use of Boromir (Captain of the White Tower version- or make sure he's got an elven cloak) and Aragorn- either one will do, but keep the smaller heroes the same. Feel free to factor in a captain of Minas Tirith or two as you need to include them for more warriors.
As for warriors, my recommendation is as follows- in smaller games, use only the normal warriors of Minas Tirith with Rangers across the board for the archers (by the way, every one of your ranger models can use his bow, just in case that wasn't clear). Use as many of the warriors of Minas Tirith with spear and shield as you can, and when people get into combat, put the spearmen behind the rangers- the extra fight value will help you clear the lines. Focus on achieving one of two things with your shooting- either killing what you can't fight (trolls) or gaining a numerical advantage. Focus fire as much as you possibly can on targets of opportunity.
At higher games (where you include both Boromir and Faramir) make use of Boromir on foot with the banner, keep Faramir nearby, and make their personal guard be the Veterans. Make sure each veteran has a normal spearman and that Faramir has a spearman as well. You can use the Guard of the Fountain Court in that unit, too, just make sure they have normal spearmen, as you don't want a higher fight value model in the back if it isn't an army-wide thing.
Use the rangers as archers, and use a combination of normal swordsmen and spearmen as the anvil for the Boromir and Faramir group to hit. Tactics remain more or less the same- the shieldwall is your friend. Use it to maximum advantage.
And I completely sympathize about the thesis.
Good luck on all fronts!