Assets like models, and textures have to be built in 3rd party programs such as 3DS Max, and Photoshop. Blender's a good free alternative to Max. I don't use it myself, but I've seen good things built with it. Really, you can use any 3D modeling program that can export in .FBX.
As for textures... I use GIMP. It's fairly robust, and I no longer have a copy of Photoshop. While there are certainly things Photoshop can do that GIMP can't...I've found them to be pretty irrelevant.
any thought of putting together a kickstarter, or similar effort, to raise money for this project? seems a rather prodigious amount of work and some additional assistance with tools, people, project management, etc would likely help.
Between MWM, H&V, APR, Valiance, and CoH revival/binary, this group has almost created the game version of marvel's movie universe...