Far as the superlaser goes, here's one idea.
Leave only a single three wide path on the map that leads to the fortress. On either side, dig a moat to be filled with lava and then have a wall on the other side of the moat from the road. The lava moat is really just optional and only if you're one of those MUST INCLUDE MAGMA types.
Now and this is a major thing as it directly affects the design of the entire fort, have the superlaser array facing towards this road. As close to the edge of the map as possible, build a ramp out of green glass blocks and continue up at an angle rotating ramps and floors upwards up until you get close enough to the Dwarf Star that you can split the "beam" into several other ones that connect to the Dwarf Star itself. After they're attached, remove the piece connects the main beam to the focusing beams.
Next to the bottom ramp, build a support that will hold up the floor directly above it and then remove the ramp.
Now, when you have Master Gunnery Chief Kronk McUrist pull the lever to fire the superlaser at Goblin scum, the collapsing support drops the beam down on the siege, creates a nice dust cloud to simulate a planet shattering blast, and the dust cloud launches the goblins into the lava moat on either side of the road. Well, except for those squished by the collapsing green glass blocks.
And there you have it, a green superlaser blast.