Always remember the main point of the game is to have fun. . . .
The GM should translate at least one of her favorite characters into Fudge from whatever system she is used to. This will give her a good idea of what traits to choose, and how many.
Fudge is incredibly flexible, possibly more so than any system you’ve played before. Once you’ve translated a favorite character, fiddle with her a bit. Can you tweak her to be exactly what you want, possibly in ways your previous system wouldn’t allow? What if you split that attribute into two or three effects ah! See, she can be smart in some ways, but dumb in others; knowledgeable of some things, ignorant of others. Hmmm too many attributes? Make some of them gifts, then that might be easier to deal with. And so on have fun!
It is easy to create NPCs to challenge the player characters by counting levels. Figure roughly how many levels have been spent on combat skills by the average player character. This figure, put into combat skills in an NPC, should give a fair fight. For example, if the PCs are built on 40 skill levels and four free attribute levels, the average character might have ten levels in combat skills directly. In that case, a gang of thugs with ten levels each of combat skills and two attribute levels put into physical attributes should challenge the player characters pretty closely.