anderledes elever = not normal pupils
forskellige elever = diverse/dissimilar pupils
Yes. This could be both positive or negative. If you want to specify that she is different in a positive way, you could say "Pigen er noget særligt" = something special.
Jeg is most definitely not a French loanword. :´)
They have a common ancestor in the PIE word "*éǵh₂", going way back. The French "je" then derived from Latin "ego" -> Vulgar Latin "*eo" -> Old French "jo". The Danish route went via Proto-Germanic "*ek" -> Old Norse "(j)ek".
So, they are related words, but then again they're not any closer than almost all the other words for "I" in Europe.
Niveau is good, though. I also remember succes.