Hi DRoam,
It depends...
Sometimes I would do this with option 2. So the Blue, Red and Green parts would be a one multibody part, I'd then push that out as a subassembly, and then place and constrain the subassembly 2x as needed in a top level assembly. Then I might create a new part in the assembly, use the Copy Object tool to pull the 2 sub assemblies down as work surfaces, and then create the geometry for the gray part using those work surfaces
Other times (such as when the gray part is actually more than one parts and they have geometry that is based on the other parts) I might mirror the Blue, Red and Green parts in the multibody part and then create the gray part(s), but then only push out 1 copy of the Blue, Red and Green parts as a subassembly, then push out the gray parts to a new assembly as a 2nd Make Components operation, then place and constrain the subassembly in that assembly 2x as needed.
And then still other times I'd push out the part, edit the resulting derived part and include more solid bodies as described here:
http://forums.autodesk.com/t5/inventor-forum/creating-multiple-multibody-parts-from-a-single-multibo...
And then also....
For parts like those red parts that have holes and features that are secondary do not relate to the "fit" of the interrelated parts, what I prefer to do is reserve those features and not put those in the multibody, but instead push out the part and create those features in the resulting derived part. This keeps the multibody less complicated and more "nimble".
Very generally speaking I prefer not to try to load he multibody with lots and lots of parts, but instead only those parts that have "fit" geometry or are driven from a common set of parameters. The common parameters situation is where I see a lot of benefit from multibodies.
And then there are setups like this simple example has one multibody part that is then derived into other part of the assembly, and serves as the "master", which allows us to piggy back off the master geometry in a way that reduces the need of handing over parameters again and again.
Volume Assembly.zip 320 KB
So, I don't know that I've cleared anything up here, but there are some options that might be worth knowing about, so that you can choose what works best, when it works best..
I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com