What are some ways players could go about robbing a train at mid-levels?

tl;dr: How would you get on, rob, and get off a train in hostile territory around levels 7~9?

I've been brainstorming the skeleton of a mini-campaign (3~4 sessions) based around a train heist, hopefully around levels 7 to 9-ish.

Important world background: the train is located in hostile Dwarven territory, powered by necromancy, and said Dwarven empire is big on necromancy and slavery. I can answer any other worldbuilding detail-related questions if necessary, but generally all first-party content is on the table for ancestries and classes. Deities are totally different but without going into detail; evil empire has a unique religion that revolves around a generation incarnation of a god-king.

The players will be trying to extract an unknown superweapon from the train, which will have a variety of car types - luxury transport, cargo, maybe a car full of military guys in transit, etc. Basically any train-related tropes are on the table.

In terms of the heist, I will try and give the players freedom to accomplish 3 main objectives however they want; 1) getting onto the train, 2) locating the target, and 3) getting off the train. I'm hoping that having these goals will help enable players to be proactive about making a plan. However, I still want to be generally prepared to enable or complicate-in-a-fun-way these plans, and wanted some perspective to try and avoid missing any obvious options.

Basically, I want to be able to give encouraging information and/or potential complications to players/characters when they come up with a plan. If they say they want to use flight magic to get on, I will be able to tell them it's definitely possible (by spending X amount) and that sort of entrance will make walking around like they belong very difficult.

1. getting onto the train

We have classics like riding up next to the train on horses and jumping on, using flight to get on, disguises both magical and mundane (pretending to be a dwarf, an undead, or a slave who belongs on the train), or sneaking on. The party doesn't necessarily have to get on as a group, so each character has a bit of flexibility in this.

2. locating the target

Maneuvering about the train without raising suspicion, whether that's stealth, disguises, or a "scouting" polymorph like Insect Form or something. Divination magic. Climbing around the outside of the train.

Identifying the superweapon will probably be done via some magic item with that specific purpose - that's too central of a question to leave up to players/characters interpreting things, and is something that needs a definitive yes/no to keep the story moving.

3. Getting off the train with the target

Getting off sneakily is a good first option but the lack of info on the size and nature of the weapon means that they might not want to risk relying on that. There's the always popular "go loud" where the party engineers a disaster on the train (if things haven't already gone horribly wrong) to distract from their disappearance. Teleportation magic might be a possibility.

Am I missing any other ways mid-level characters might go about these three objectives?