(re: Sierra’s Game Creation Software) Sierra used lots of different tools through the years – so there is no easy answer to this.
In the early days we had our own art tools. For the adventure games, we primarily used an animation editor/sequencer that we called “the view editor” which was somewhat like the editors used for animating gifs today. I believe we had some amount of inter-frame compression, but not much. It was essentially a tool for sequencing a series of animation cels.
For 2d animation, towards the end, we would pencil sketch the animation, then use Photoshop to do the painting. For 3d, we used 3d Studio Max.
As to the project that we are going to build, I see a couple of steps:
We need to decide if we are 2d or 3d
We should look around to see what is available in todays world — and, what we can get for free, or cheap
-Ken W