First, welcome to the boards!
I'm currently playing a contracted kandra and acting as the groups spy master, so have gone for various sets of bones. So far I've maxed my Fast Replication and have just maxed Chimera as well. While re-reading Chimera some thoughts came to mind.
Wow! 24+ advancements is nothing to sneeze at!
1) From the wording I don't need props for the aspect I include, so in the example about the dog that talks, I don't need human props, I just have to had taken a human form.
I'm thinking you mean bones where you use "props", right? You're not using "props" in reference the game term, correct? To answer, I would say that it depends on what characteristic you are attempting to create. If the characteristic requires a certain set of bones, I would say that you need the bones. The example you use of a dog that talks wouldn't require any additional bones. Giving a dog form opposable thumbs? I would require some additional bones and probably implement some circumstance modifiers.
2) When taking a form do you use the form's physique or your own. I know in the book that TenSoon is reluctant to take the form of a dog but comes to like it as he can keep up with Vin. Is this from an increased physique or an appropriate trait from the dog.
I would rule it as a trait from the dog, if necessary, though I would likely not even bring it up unless it served some story-related purpose.
3) Say for example I was following someone and lost them and decided that to find them again I could use their scent, having previous taken the form of a blood hound. Would you say I would have to re-apply the form with this trait, reverting back to my natural form or that I can just add it in.
As worded, it seems like you can only grant additional features when taking form. Maybe it has to do with tying the various systems in the body together with the new feature(s) being more complicated than simply creating the new feature(s)? I'm trying to think of an example from the books where a kandra adds a feature after
forming the body, but I'm drawing a blank.
4) In relation to 3 - we have gone with the second option and said that the normal time needed to take on the form that the trait is from would be how long it would take to gain said trait. So for example if the blood hound was physique 3, then it would be 3 hours or 3 minutes with appropriate stunts.
Which makes it little different (as far as time is concerned) from the other option, right? I guess that it would be easier to conceal the (potentially grotesque) changes taking place, if that makes a difference. I suppose it would be at dinner time!