Take 2: How to thicken walls of a hollow non-geometric model

[bryn.parrott]

So, this is take 2 of dealing with this issue.  The attached 3 photographics images refer.  The objects will be scanned into stl mesh files and then need to be manipulated to attain the following goals and constraints:
1. scale the objects to 2/3 of original size.

2. Thicken the wall between the inner and outer sides of each object and this refers to the topological shape of a bowl.

3. Retain the objects form, including the shape of the current division between the two parts of the object.

4. The "head" of the dog is currently and is required to retain 100% infill (a solid object) and ditto for the "tail" part. 

I learned a lot from the first pass at this, but the main thing is that Fusion 360 seems unable to deal with directly thickening the walls of a model that is topologically similar to a dish shape, having two main parts, one convex, the other concave, the concave nested within the convex and joined together at the top.  When attempting to set the wall thickness of such an object Fusion 360 will attempt to thicken the walls between the inner and outer shapes.  Fusion 360 can, however properly adjust the wall thickness of an object that is topologically similar to a closed cylinder.
So, thats the background.  Here is my proposed plan of attack, based on my limited knowledge.
1. Scan the object as it stands, in two "halves".
2. Insert the mesh files into F360 and process the stl files for aberrations caused by scanning - close and stitch holes
3. copy the object (for safety). Further operations to be based on the copy object.  Scale the copy to 2/3s its original size. (requirement 1).

4. create a further copy (3) and process the copy to create a solid object (including face groups), and "convert Mesh".
create construction planes and use to remove the head and tail parts of the object, leaving the main body of the object.

5. Create a sketch and use the sketch to map a profile of the upper side of the existing cut (length-wise along the object).
6. Repeat (5) to create a profile matching the lower side of the existing cut.  (this may be the same shape, in which case this step is not needed, just thin extrude the upper side profile.
7. Sweep the two profiles together to create a "flat" surface that is 3 dimensionally curved.  This is to be used to cut the object along the same lines as the original shape, after joining of the two halves for wall thickening.
8. Take copy 3 and join the two halves of the object together using combine, ensuring no gaps along the join line.
9. Use the shell command to get F360 to hollow the object producing walls 3mm thicker than current.
10. Use the cutting object from step 7 to divide the object once again using combine.

11. Rejoin the head and tail objects that were cut off at step 7. 
12. Additional steps are needed to correct the 4 x holes and threads in the sides of the object that are used to hold the object together.  The size of the holes were reduced when the object was scaled.

Notes:
(i) I am unfamiliar with creation of a thin extrude, and using one as a cutting object at step 10 in the combine function, so I cannot be certain this will work.  The reason for using a thin extrude is because the existing cut on the object is not uniform, having a 3 dimensional curved shape.
(ii) I am not completely certain F360 will cooperate with the shell command at step 9, and allow the walls to be thickened in the way I am expecting.

So, my questions are:
(a)  are there any steps in the above workflow that will not/cannot work in Fusion 360, ie the steps do not all work in the way I am expecting them to work.
(b) Is there an alternate/more efficient workflow that will result in the desired outcome, meeting the goals outlined in the opening paragraph ?