Would I be allowed to use a library of sound effects, assuming I mix and rework them in some way? I'm unclear on what constitutes creating something from scratch. Another thread said we could use music samples in FL Studio, but that seems like the same issue.

Same question here: can I use the music created during the jam from preexisting loops?

Using samples are allowed for music, if you're using them for music effects then not so much unless you modify them.

So if I want to add sound effects (like footsteps), I have to record these myself or use music intruments, right? 

(I can't find a clear answer to that, and I've read through all of the posts xD) 

Correct @Daito

@FunArtTM sfxr is allowed