I need some help, but first I'll catch people up on the situation:

So, we're nearing the end of my custom campaign, and the group is about to tackle the big bad thing they have to do: sneaking onto an imperial star destroyer to plant several bombs as sabotage before a larger attack. So far, they have convinced the local crime lord to give them some under the table help because the imperials have been crimping his business, and assured him he won't be implicated. His help has come in the form of two stormtroopers that he has on his payroll (this star destroyer has been docked here for weeks and this gangster hasn't been idle). They have been told that the PCs just want to get into the cargo hold to steal some things, but they think that is all. These guys will let some people do small crimes and help them get away with it for a price, but they aren't about to betray the empire in a real meaningful way.

The PCs plan on disabling them somehow once inside and then getting around. They have an access card that will let them into most areas of the ship, some less-than-perfect stormtrooper armor to wear, and a piece of hardware that will let a slicer get into a computer remotely if they plug a chip into a machine by hand.

Now, here's where I need some help. I don't see it being too much of a problem for them to disable the guards once in the cargo hold, but they really aren't supposed to be there and they aren't exactly military types so someone is bound to notice them soon enough. I need some modular things they can do to get around the ship and plant these bombs (in the shield generator, targeting computers, etc). They have a great slicer on the other end of that chip, so if they plug it in I want him to be able to do things for them, but also not make it easy mode either. The general theme of this campaign so far has been "idiotic stumbling to victory" so appropriately awkward ways to succeed are definitely ok.

I have a few ideas, but they aren't very well fleshed out yet and I figured this community has helped me idea generate before for this sort of thing so I'll try again. Any seeds of ideas are more than welcome, I just want this mission to feel a bit more fleshed out in terms of mechanics and things to do, as it is sort of the 'climax' of the campaign. Thanks!

Star destroyers are very large. Getting around takes time. Turbolifts make all the major areas accessible, but are of necessity high-traffic areas where your PCs are likely to be noticed. So the obvious alternative, getting around on foot, takes time.

Getting Out of Sight - They've come on board with the help of their two stormy pals. Now they have to deal with the rest of the 10k+ crew. Stealth checks, plus perhaps a Knowledge check on Imperial procedures helps them get somewhere out of sight where they can then begin their infiltration.

Finding the Route - The PCs are now in a little-used storeroom, empty office, tertiary maintenance area etc. They (presumably) have blueprints of an Imperial Star Destroyer so they know what routes they can take. But now they have to examine those routes and compare them to the activity they are currently detecting. Also, on a ship this large, many spaces are probably repurposed from time to time for a variety of reasons. Their first slicing foray might find that the abandoned storeroom next to one of their targets is actually being used as a secondary lounge for TIE pilots. Some of these discoveries won't be found by slicing, but by stumbling (since the new/alternative purpose might be "unofficial").

Getting Lost - Even with blueprints and sliced access to maintenance schematics, routes through the bowels of the ship aren't straightforward. Maybe if the ship was newly assembled, but if a ship has been through a battle or three, then repairs and maintenance probably aren't 100% properly logged. "Turn left at the next junction." "Uh, there's no passage on the left."

Droids are meticulous for maintenance, but occasionally unreliable. Access panel labels might be mislabeled, swapped, missing, or placed where there isn't even an access. "Ok, you need to disable the sensors for the next ventilation shaft. Look for access panel 12D-147H-14X, should be on your left." "There's a 14H-47X." "Ok, open that. Look for 3 blue wires attached to a power converter." "Um, all the wires are yellow, there's dozens of them."

Unexpected Encounters - Lots of these, from random encounters with strolling crew, to unscheduled patrols, to unlisted or unscheduled maintenance in the middle of the PCs route.

The Suddenly Important Side Quest - "Hey, doesn't that voice sound like the girl we met two days ago?" whispers one PC. Other PC nods and glances down through a small vent, going pale. "She's in an interrogation room." Do they care about this girl? Should they? Perhaps she knows something about them or their plans.

One Way Route - Due to some complication, part of their route in cannot be used in the other direction. Maybe the fan control for the vent shaft is only on one side of the fan, and approaching from the other side means no way to shut it down. Now they have to find a new route to get back.

Shielded Zone - This is an Imperial warship, built and maintained by a very security conscious, if not downright paranoid, bureaucracy of designers. Some areas are going to be shielded in a variety of ways. So the PCs confidently plug in that slicing access chip... and nothing happens. They're in a com deadzone and the signal can't get through. They're on their own for this one...

Rebels? - I'm assuming your PCs are with the Rebellion. But you mentioned a crime boss helping. So, if they're Rebels, then they bump into another group using part of the same route that is there to steal some weapons. If your PCs are independents, then they run into a group of genuine Rebels. Either way, they suddenly encounter another group of infiltrators doing a different mission that is, perhaps, not exactly compatible with theirs. Maybe this second group is noisier, more fanatical, or just more callous and has caused a security alert. Maybe they'd really like some of the explosives the PCs are carrying. Maybe they want to remain secret and silencing the PCs is their chosen way. Maybe they think the PCs are great and want to help them, but aren't particularly skilled (they've been lucky so far). In any case, encountering another group sneaking about the Star Destroyer at the same time as the PCs; well, what are the odds...?

Sir, I owe you a beer. Those were fantastic ideas, I ended up squeezing nearly all of them in. I had little time to prepare for this session, so your help was a godsend. Much awkward and stumbling in, part of the group getting arrested and subsequently broken out and heading down a trash chute episode IV style... and they only planted 3 of the 4 bombs. Next session should be the real end of the campaign, and it is setting up just as I'd hoped .