Can you jump diagonally? For example can you jump in one direction and then change direction mid jump as if you were jumping diagonally since movement is done orthogonally? I was watching a guy playing and he had an enemy jump 2 spaces but it was one space forward and then one space down to get to another space (sort of like an L shape movement) Is that legal?
Yes. You can look this up in their FAQ, including a nice picture for clarity.
When Jumping, do I have to count spaces out in a straight line?
Jumping still follows normal movement rules, other than it ignores Effects from all Terrain other than Obstructing Terrain. This means that you can count out the spaces in any pattern you’d like before you decide to make the Jump Check.