I tell you the truth: the campaign you describe in the OP is my Dream Campaign.
I grew up in the 80s. My first D&D adventures were Keep On the Borderlands and In Search of the Unknown. Basic and Expert D&D had tables full of hirelings, and the game presumed that you had henchmen. Growing up, we regularly set out on adventures with over a dozen NPC hirelings, and straggled back to town with 2-3 survivors. Very rich survivors, since they each got a quarter share of treasure.
That's D&D, to me. Exploration and adventure. More like the Age of Discovery, with key individuals leading a long trail of porters into some godforsaken place. Rather than some costume drama where so-and-so is "the chosen one", and this guy's a reluctant hero, and that dude's dad is a major NPC, and blah blah blah.
No. The only motivation I want or need is "there's a big blank spot on this map. We don't know what's there. Go find out."
Which is why I almost misted up reading your post. Creating a budget, laying in supplies, estimating consumption (and adjusting for expected attrition), hiring and equipping henchmen, setting watch schedules and patrol patterns, formulating standard operating procedures for anticipated obstacles and crises?
Oh yeah. That's my jam. I'd play in your game in a heartbeat.
One suggestion: kill the player characters. I mean, don't be unfair. Don't be cruel. But let the dice fall where they may, even if it results in a TPK. When (not if) a PC dies, promote one of the hirelings. The new character will already be familiar to everyone at the table, and have a reason for being there.
I even encourage you to go a step further, and to consider the expedition the player, rather than the individual PCs. It's the success of the mission that matters. Level up the adventuring company. That way, when the survivors make it back, some can retire, some can go off and start rival companies, some can stay on--but the group, as a whole, has continuity. You can then have fun advancing the timeline 1, 10, 200 years into the future. That long-lost faraway ruin is now a settled trade hub. The forbidden temple where Jorich was killed by the Lich is now the Duke's palace (and the Company knows the location of the secret entrance to the high priest's tomb, now used as a treasury). And so on. Minimize attachment to individual characters, and maximize attachment to the setting and the world.