There's a discussion on creating custom moves that represent difficulty, first thing in the Advanced Fuckery chapter (p. 268-9). You've got the basic idea already, and your suggestions map right on to some of the ideas. To summarise the ways you can made a move reflect a difficult task:

• You can make a general move that lets you change the difficulty with a -1 or -2 when "things are tough", but most groups find this custom move boring/annoying/not a valuable addition. (This one isn't relevant to you particular case but here for completeness.)

• You can cover difficulty into a more specific, but still general "when the NPC is strong" move, treating it like the NPC is interfering with a 10+, giving the PC's roll a -2. This is a totally legit thing to do as the MC in Apocalypse World and matches one of your ideas. Just give them a -2, because reading Uncle Richard is just that hard.

• You can make a move that just layers itself over another more basic move, modifying its outcome. Something like, "when you're trying to read Uncle Richard it's acting under fire, and the fire is: Uncle Richard is disappointed in you." This can have whatever variations you can think of, and is just like one of your ideas.

• You can roll difficulty right into the substance of a move, saying "when you read Uncle Richard…" and then giving a new, more interesting, tailored, but ultimately fictionally disadvantages list of options on 7-9 and 10+.

  You can mirror an existing move or make it a subset of options, as you suggested above, but to do it cleanly just crib the options and make it a move all to itself without mentioning the basic move. If you want to do it with style, change the options so they reflect the idea that this move doesn't get you want so easy, making the choices tougher, meaner, and more interesting in their focus on this particular person.

All that is to say, you've got the right idea: make a custom move, however you like, to reflect Uncle Richard being damn inscrutable. Either just make it work, or make it cool, but make it.

And of course, you can always just say, "Yeah, ok. But doing that is Acting Under Fire and the fire is Uncle Richard is disappointed in you." That's just fine for ad hoc difficult situations. When you're finding you want to do that every time a particular circumstance comes up, then that's exactly when you should be (as you were) thinking of making a custom move for it.

A one-shot session of Dungeon World is pretty trivial, actually. So far, all games of DW I've played have been one-shots. All you need to prepare as DM is a short adventure, typically a dungeon. You don't need to deal with Fronts at all, and setup is the normal quick character-creation process of throwing the playbooks at the players and asking them to fill in the blanks. You just run the game like it's a First Session (p. 177), except that there won't be a second session so you don't have to do the After the First Session exercises. The checklist of goals on page 180 is what you should focus on.

To complete an adventure in a single session, you need either an adventure that you've got a really good handle on how to pace to fit, or design (or borrow) one that has an open-ended, players-decided goal. A dungeon that they can choose to back out of at any time is one example of such an open-ended, player-controlled adventure. Completing an adventure isn't really necessary, but something you can try if you want. The players will have fun regardless of whether the adventure concludes. The worst that can happen is that they ask to play again to find out what happens next, right?

My first experience was with Tony Dowler's Purple Worm Graveyard: we started at the doors of the dungeon, and the objective was to return home with wealth or die trying. As it was a convention game, we could choose at any time to back out and take "home" whatever wealth we'd found. (Not that we couldn't have done the same in a non-convention game, but it was helpful for the DM to say we could do that explicitly so that we could have a satisfying conclusion within the time allotted.) We didn't explore the whole dungeon (and it's not even a very large one), but we had lots of fun, enjoyed the open-ended options of the game just fine, and escaped the dungeon with a satisfying amount of loot and intangible discoveries. In a two-hour session we got through seven chambers, so a budget of 15–30 minutes per room is probably a reasonable rule of thumb when you're drawing a dungeon for a one-shot of DW.

My second experience playing DW (also at a con) was an investigation adventure that involved a town, a mayor with secrets, and a church. We didn't finish the adventure in the time available, but we had a lot of fun and thoroughly enjoyed the open-endedness and player agency that DW offers. I would have liked to finish uncovering what was going on with that cult, but it didn't detract from enjoying the play process in the least.