Yes, it runs really good on the 32GB iPad Pro. I am running it on the 32GB iPad Pro 12.9 and not having any issues with it at all. I purchased it just for Shapr3D a couple weeks ago.
So far I see no reason to need a 128 GB or 256 GB version unless you need the storage.I solved that by exporting designs to iCloud and moving them to my MacBook Pro then to my SAN for storage. Even after a few models, some other apps I still have about 20GB free on the iPad Pro.
As Istvan mentioned, don't forget the Apple Pencil.
NOTE: I tried the app on the smaller iPad Pro and found that I had to be sure I closed other apps to free up the RAM some. But more importantly I found that I needed the screen real estate that the 12.9 offers, the extra RAM was a bonus.
I also realize this is an old post, but I wanted to share my experiences as I am new to the forums and it is likely others will have this question as I did as well.