Any tips to plan/create large scale battles?

So ironically this is my first time DM-ing (wow, the new guy wants to complicate things on his first try) and I wanted to give my friends a campaign set in The Lord of the Rings universe because in the multiple games we've played together, they've always mentioned wanting to become generals or commanders and I thought I could provide them that experience as well as finally experiencing what it's like to be a DM.

I'm currently planning my campaign and am using the Adventures in Middle Earth as a guide to world build, make items etc..., I've even made a rough draft of the story line and what I'd like my friends to experience as players. It's set during the war for the one ring and I'd like to lead their own arc as a party to be part of the various large scale battles of that time (battle of Erebor and Dale, siege of Helm's Deep, Battle of Pelennor Fields etc...) while being separate from the characters of The Fellowship of the Ring 90% of the time.

It's a lot of ideas in my head, but I never really sat down to think about how I'd plan them, so far all I've got is whenever they're going to fight in these battles, I'd have two battle maps, one "zoomed" and another one that stretches the whole battlefield. As a party, they'd have their own enemies (and ofc big bad guys) to fight (typical dnd style combat) and after their individual turns, they get to play as commanders and position, large groups of soldiers/siege engines etc... and attack other large groups of enemies or defend special areas or chokepoints where the small battle hosts they control also have their own stats, special abilities and such. (Both micro and macro managing the battlefield as they fight)

My only fear here is that this method might get them a bit too disconnected from their soldiers and they'll just see it as two fight rounds with different characters which might bore them. Any tips on how I can change/improve or add things to this current plan is well appreciated, cheers!