Planning a Blades in the Dark one-shot

I'm travelling to see friends this weekend, and since I finally pre-ordered Blades (and have been listening to Rollplay: Blades) a couple weeks ago I offered to run a one-shot while I'm there - I threw out a few game ideas but one of the players latched onto my suggestion of a heist game in "basically Dishonored the RPG" so that's what I'm planning.

I just finished reading the whole book a couple days ago, and I've been thinking about the game, so I'd appreciate any suggestions or feedback anybody has (although from asking elsewhere I know the first suggestion will probably be "Blades is about improvisation, don't plan a heist, just make it up based on the players!" - I've only run a few games and I already know my biggest weakness is inventing new things on the spot, so yes I am going to plan at least most of the scenario and let the players do what they want in it).

None of the players had heard of Blades before (at least a few of them have experience with D&D but I don't know the rest) so my current plan is this:

1. Start with premade characters. Give them an overview of the setting and the playbooks and let them each pick one. Ask a few background questions about their characters

2. Throw them into the middle of a fight - basically, as if they had gotten a 1-3 on an Engagement Roll. Maybe even start with one of them getting shot.

3. Once they finish the fight they get loot, including the main objective they came for, a <map/letter/journal?> that they've heard will lead to a huge, retirement-level score.

4. Character customization - now that they know how the game works, let them rearrange their action scores if they want to, and give them a couple more dots and one more special ability. Ask them about their contacts, rivals, etc.

5. Downtime while one of them (or a cohort) deciphers the clue. If they got beat up or stressed in the fight they can recover, otherwise they can acquire assets or gather information on their next score. They'll have a few coins each from the previous score for improving their results or taking extra actions.

6. Plan and run the actual score as normal.

This accomplishes a few things - in the first score, I can not only introduce them to the basics of action rolls, I can push them to use features like flashbacks, resistance rolls, and inventory. eg, "Well, Cutter, you just broke into a hideout of the Grinders, and you're staring down the barrel of a pistol. Fortunately, the Spider got some of them out of the hideout first so you're not facing the whole guard. Spider, let's have a flashback to see how you did that." I'm hoping that by introducing those ideas up front, they'll realize how flexible they can be later when planning their own heist and not get too hung up on contingencies or inventory. Second, they can customize their characters, but they'll know how the game works and how to use at least some of the skills so they won't be guessing. Plus, I just really like the downtime activities (and the possibilities for entanglements and overindulging vices).

A few things I'm unsure on are XP and the Crew sheet - I don't think they'll get enough XP from desperate actions to fill any one track and I don't want to do roleplaying XP in the middle of the game, so I may just skip it. But I am worried it will remove one of the incentives to take crazy risks and push for desperate rolls, as well as to express their characters in interesting narrative ways (although the latter is hard to do in a one-shot anyway). And the book suggests not using a crew for a one-shot, which would also simplify things, but if I give them a Shadows sheet during the character customization part, I could let them pick two abilities from it (and some of the Shadows abilities are pretty cool). Although it also might make them feel like they need to sneak into the main score, even though I'd like to give them the opportunity to take any of a number of approaches.

For the initial score, I don't have the details nailed down, but I basically want them to be stealing something from another, bigger gang to lead to the main score. The Lampbacks or the Grinders or somebody like that. For the main score, partly inspired by the Wraiths write-up in the book, they'll be looking for a leviathan hunter's mapbook (which is incredibly valuable to a rival leviathan hunter) from an old heist gone wrong - lost in a new construction site, which is now a rich person's home (either mansion or townhouse, townhouse in Nightmarket would make sense for new construction and keep the scope small, but a mansion would give more rooms to explore and more security to have to bypass). They'll have to get into the basement somehow, as that's where the original thief was last seen hiding before being (shot? sealed up? not actually mentioned in the journal, just where the prize was left? Maybe they'll only know about the thief if they gather information). If they gather information, they can get a general idea of the layout of the home.

There's two twists. First, the basement is actually a private garden - it's a rich [noble/merchant/something?]'s pet project, with a dirt floor and a radiant-energy-infused tree in the center of the room. The walls are painted blue like a daylight sky, and the bark of the tree looks normal but the leaves spread across the roof are glowing like light bulbs. Underneath, there's a grassy circle with a bench, some planters of herbs, peppers, and tomatoes, and a Hull with a marble chassis - basically a robot butler/gardener that looks kind of like a statue (with joints). The hull will question why they're there, but won't attack unless they start wrecking the garden (unless they disable it or make a convincing argument they're supposed to do it first). They'll have to break through the wall to a sealed-off closet to get to the prize. That's where the second twist comes in - once they knock down the wall, they'll release an angry ghost of the thief (a wraith of the Wraith, heheh), who died down there and was sealed off before his ghost could rise and further sealed with runes once he started making a noise. However, despite being sealed he's grown powerful as he waited and sought vengeance, especially so close to the tree, a source of electroplasmic energy. At that point, they can try to fight the ghost (or reason with it, or command it) in a room full of energy and a hull that they or the ghost can manipulate in weird ways (especially a whisper or maybe even tinker) as they come up. If they deal with the ghost quickly, the bluecoats can arrive while they're in the basement, or the ghost can be the climax and they can make it out quickly once it's dealt with.

In addition to just liking the idea of this underground garden in a city of darkness, this gives me a good variety of obstacles for the players to deal with: thugs (in the initial score), guards (if it's a mansion), sparkcraft (maybe even a sparkcraft door into the basement), an angry ghost. The players can make their initial entry by sneaking in, talking their way past a servant, bribing the servant, or kicking down the door if they want to.

Thoughts? Suggestions? Should I keep the entry simple with a small townhouse or drag it out a little with a mansion with guards? Draw out a basic floor plan for them to plan around or just wing the layout once they start? Any way to spice up the opening scenario, or good details for the specific characters?