First issue was related to texture being in DDS and not PNG format. I had to manually convert the texture files.
Second issue was due to localization. I use "," instead of "." to separate thousands places.
Also, the instruments are all outside the capsule and way too big.
I am using the .unitypackage from "PartTools_AssetBundles_2019.4.18f1.zip"
I have configured and set the GameData directory in the Part Tools Setup tab.