I fall into the camp of “incorporate anything that doesn’t require a painful change.”

Our group structures the story arcs like the book does, a few days/weeks of action separated by long stretches of down time.  That has allowed us to incorporate the end of Changes without any real stress, no one had any hooks with the Reds and Harry hasn’t shown up on screen.  On the other hand, if Lara Raith manages to get offed in a future book I’ll probably elide that as long as possible since one of my PCs has an important relationship with her.

I kind of like that it allows the sort of very close very long fights you see in movies, ones that last multiple scenes over dozens of exchanges.

Having played SotC I can testify to the fact that there's a fine, fine line between "long" and "dull." 

That's certainly a more granular and tactical approach to Fate combat.  If that's what floats your boat have at it, but personally I like the fact that the system is fairly abstract and the player/GM can narrate outcomes to suit their particular taste in fiction.

Now, is it true to historical fact when the guy playing a barbarian describes how his massive axe?  Of course not.  Is it fun?  Yep.  The great thing about an abstract combat system is that it allows people to focus on the character concept and interesting description rather than picking the optimal mechanical course of action and sticking to it to the bitter end.

Now, if you want to provide some balance to top tier weapons (the way that D&D 3.X had simple, marital, and exotic weapons, with each weapon being roughly equivalent within it's class) you could maybe apply a defense and/or initiative penalty to big, unwieldy, but devastating weapons while applying a bonus to one or both for smaller, less damaging weapons.  If you want to avoid "modifiers" you could say that "unwieldy" weapons take a supplemental action to ready, so if you want to attack continually with them you'll take a -1 to your actions going forward.

Well since this is a medieval fantasy setting "speeding vehicles" probably aren't on the table.

OP said he's planning on giving out more stress boxes, and weapon rating are only meaningful in the context of how much damage it takes to get to those tasty, tasty consequences, so a Weapon:5 axe might not be that overwhelming in his hack.

[edit] Forget what I was saying about aspects instead of rules, those work just fine as stunts.

"No, you cannot intimidate the gazebo," or, "No, you cannot seduce the fire truck.  Cut that shit out," are both the correct way to go.

QFT

You want to see the Stormtroopers living up to their reputation, look at the Battle of Hoth. Yes, numbers played a part, but there's a reason that the rebels are running for their lives.

Yep, because the Rebels were minions too, just crappier.

In the Fate games that have minion rules, they're generally rated from Average (+1) to Good (+3,) and have a number of stress boxes equal to their bonus.  Instead of acting as individuals minions form groups with one action, but receive a bonus to that action based on the number in the group; 1-2 get +1, 3-5 get +2, 6-9 get +3, and 10+ get +4.  If you rate Storm Troopers at Good, that means a squad of 10 acts at Epic (+7), which is pretty terrifying.

I'd strongly recommend adopting the minion rules from SotC.  Storm Troopers drop like flies while being fairly harmless in less than company strength.  The rules should reflect that.