For the benefit of readers, a "neo" jump is the same as what Mason is referring to as a "Mid-air strafe." A double neo would be that but two solid blocks between.
You don't reach maximum walk speed instantaneously, but there is a very quick buildup before hitting max speed, so if you jump right as you begin pressing forward you won't go as far. Take a small amount of time to walk the direction you want to jump before jumping for maximum distance.
Not sure what you need to know about head hitters. They are possible, you just need to jump at the very last moment.
Strafing doesn't make any difference as to how far you can move (the movement vectors produced by WASD are normalized), though it may assist you in neo jumps if you can't do it with screen-turning alone.
Collide boxes are always cuboid shape and do not rotate, so you can use this info to understand a bit about what angles you need to take when jumping.
As for double neos, these are just not possible with the default speed you can move at in ClassiCube.