[Suggestions for my (first)project]

If you replace the contents of an Outfit the new stuff may not show up on an existing saved game.  

[[Sky] About Talking Activators]

If you can do the dialogue you can open an inventory, the trouble is you do need to be in a faction to have access to a chest to hold the inventory to display. There is probably a way of scripting the whole thing but sounds tricky to me.

[[Sky] About Villages - what to include?]

I would say as a rule of thumb you need more normal houses than there are shops etc.

[[SKY] Weird Merchant Issue]

Create your own faction linked to your own food chest don't use the ServicesFortSungardFoodMerchant faction because that has a quest condition on it.

[[SKY] Weird Merchant Issue]

That usually happens if you don't add JobMerchantFaction.

[Missing Lod Textures on Mountains]

I've generated LoD for a lot of worldspaces multiple times and fortunately so far Oscape and TESVLodGen have not let me down; but you never know.

[Missing Lod Textures on Mountains]

Oscape does not generate object lod files; the ideal combination for a LOD is Oscape for the terrain LOD and TESVLodGen for the Objects and trees. The CK will do objects and trees but it is very buggy and often makes a hash of it, including giving you purple mountains.

[[sKY]Vendor Issue]

Not sure about male nord -  if the voice type can't say the lines you won't get them. Try Male Brute that can say BSmith lines, to see if that is the problem.

[[sKY]Vendor Issue]

You haven't put him in JobMerchantFaction - which is the faction that has the merchant dialogue

[Random Patrol Actor]

I don't know if you can call a package on a spawned NPC in a script, but I have never tried to do it; you could try adding a package to the NPC you were spawning (obviously copy a vanilla one)

I don't tend to do it this way - I usually would have the NPCs as quest alias' and attach the package to the alias. I trigger the quest based on the location or locations that the player enters via story manager. It then requires little scripting - just a few fragments.

[Painfully basic question I'm afraid but I can't add new topics of dialogue]

You are doing the right thing assuming you are in one of the dialogue windows. If your not getting a small dropdown box to select from it sounds like the CK might be screwed - try verifying the CKs tool cache and failing that reinstall.

[Question about horses and navmeshing]

I use a patrol idle marker with a sandbox package on the horse with a radius of 20. Seems to work OK, the horse occasionally wanders out but then goes back in. The navmesh in the stable needs to be wide enough for the horse to turn round otherwise it  trys to climb the walls.