1% critted

Also remember that (I may be wrong about this), promoted classes have a lower priority in attack turn under unpromoted ones, unless there is already a planned 2 hit KO from two units. If you position someone with high defense, that can't kill the cavs with the paladin, or with enough defense unequipped, you can stop them from being overwhelmed. After that is a matter of sending everyone else to the left, since the rightmost knights won't get to where you are two quickly. The left most group with the bow knights move at turn 3, and the right most bow knight will move at turn 5. I'm not sure at which turn the enemies at the ship move since I always aggro them, but you can aggro only one side ( like the paladin and 3 cavs in the left bridge) without aggroing the boss. The first turns are the hardest, after that it's all about proper position and that starting chokepoint, abuse the hell out of it. Hope this helps.

In my experience, Donnel in vanilla Lunatic is actually a good unit if you know put enough effort into him, even in a no DLC run. If you trap the archers in paralogue 1 with 3 units, Donnel can gain a lot of EXP from them. You can get him to level 5 in that chapter just with that method. I forged him a bronze lance after the chapter, and fed him every kill that I could. I had him at level 10 in chapter 6 and reclassed him using an anna second seal. After that he was unstoppable. But in a resources/exp distribution way, Donnel is worthless and other exp can go to better units. I've finished Lunatic classic 5 times now and Luna+ twice. But I always use a party of 6 early game units (3 couples) if I use Female avatar, and 8 early game units if male avatar, and then use add their children to the party. My first two runs I tried training a lot of characters but it was a no-no near chapter 20 because Chrom was way underleveled. So I've never finished it using only early game units and training them in the main game but hey, at least I had a full endgame party.