Here's my take on it. I've changed the mission briefing to give it more of a backstory, given the player more colonists, and, well...
Currently, the mission briefing text doesn't fit in the whole text area, you'll need to click inside of it and press down to see the rest. Then again, it's just "good luck", so there's not much of a need to. I'll need to ask BlackBox about how to increase the size of the text area.
Edit: Slightly updated this version. The mission briefing dialog is bigger now, I tinkered with the difficulty multipliers (amount of colonists, metals, and food should be about the same as the previous version), and each of Plymouth's defenses only have a 35-65% (depending on the difficulty) chance of being dual turret.