First of all, thanks for making such a great modpack :D
The magma island has a rather "nice" early game exploit:
if you put the crystal fluid in a clay bucket, the bucket turns into an iron bucket. Easy way to transport lava, and not really intended, I think :)
Also, I think the "difficult" start (magma island) is way too easy, as you will never need the first stage of combustion or a cobblestone gen (even easier with the early hopper). Dont really know how to counter that, just a thought.