Welcome to the Dune madness!
Very jealous. Mine are both into fantasy (which does mean all my old book series are now being devoured) but no interest in sci-fi.
I have also not set my Dune campaign on Arrakis. They have an option to go there, but so far have studiously ignored it. We are happy forging the History of House Sindri completely separately to the events of the Novels.
For the questions I can only answer from my perspective. Dune is a very flexible system (Great for me, not so much for some) so the divisions between skills and similar are not so clean cut at times. The situation can alter things.
I would default to Move, having said that for the crashed 'thopter I would probably allow Battle if the player had an appropriate focus of say “Camouflage”.
Again I would default to Communicate, but a persuasive argument could be made for Understand. Both would feel appropriate depending on just how the spy is working.
In these situations I have gone for Battle. Generally if the fight is imminent I have used Battle, otherwise I have gone for Understand. But not a hard and fast rule in my game.
Summary for Skills. There are normally a couple of options you can go for. Either can be right depending on the situation and your players focuses, etc. If my player gives me a good spiel I’ll often go with it.
A Q1 weapon would have 2 effects in the combat. It reduces the difficulty by 1 (Very useful against those pesky shields) and increases the damage done on a Major NPC by 1 (So 2 (Base) +1 (Quality) = 3 Damage)
Defeat is just a catch all term given how loose the damage system is in Dune. I run my games like a TV series and unless it is a plot element characters normally are just seen the following scene with a few bloody bandages and are happily running about and escaping their guards freely.
Of course you can just say that all Melee Weapons in your game have the keyword ‘Deadly’ and cite that to apply to a trait of injured if a player is defeated using one of them.
This Talent is basically the equivalent of spending 2 momentum to create an asset. In and of itself you are right, it doesn’t give much benefit (Traits aside). However, the other thing you can do at this point is spend a further 2 momentum (4 total) and make it a Q1 asset (Clearly the chair was made of mahogany). So the talent gives you a 2 momentum saving on creating a temporary Q1 asset which is mechanically beneficial.
I’m not sure I understand the question here. Normally I use my Threat to make the specific opponents appear.
I start with a pool of Threat (Normally 10 as I have 5 players from a Minor House) and it grows from player actions. I then use it to telegraph major scene elements (More troops, a Major NPC suddenly appearing, etc…) or boost the effects of the Major NPC. I can do most of that stuff without it, but I use it to tell my players things are escalating.
- Just read the rules on Threat again (pg 155) and you are right there is a ‘Threatening Circumstances’ rule where the arrival of some NPC can generate threat. (I learn something new each day
)
For how much… 
1 or 2 per Saudakar? They are scary enough without needing to boost your Threat too much. I guess it might depend on how much your players have been boosting your Threat pool and if you need to replenish it.
Feel free to keep asking questions of the Hive Mind. We can normally give you about 3 answers to any question. Sometimes we even agree on them…