For your own personal use i would recommend Olympus 2207 critter art, than can expand your variety base significantly. Ant it is a top quality content. I also asked devs if i can use it for a public project, and they approved. They have english support forum too.
Adding stuff in Fonline generally easier than in Fallout 1/2, you can edit prototypes by hand, using any text editor available. I would recommend notepad++.
Also, when adding critter art, put it into a zip archive. Easier to handle that way)