This was always my favourite level.
Here's my standard starting tactic:
1. Send an engineer pod to flak drone 1
2. Warp out to a position just to the left of Bunker Stn out of range of its weapons 1 and hold position. This is Assembly Point A. The Cantharians will attack Bunker Stn 1 and usually neutralise it.
3. Build a gunship and add it to your cruiser.
4. Build an assault transport and target it to flak drone 1 (which will be yours by the time the assault transport arrives)
5. I transfer my control to the Gunship and then build cruisers to add to my fleet.
6. Kill any engineer pod that moves in on your flak drone
Generally the two Cantharian assault transports die before they can capture the bunker station. So you can ignore them. When they do die the Cantharian carrier leaves after the station is neutralised.
6. Move in and take control of the space about the bunker station and order your Assault Transport to capture it.
You have now secured the area.
Watch out for a steady stream of Cantharian engineer pods heading for your flak drone.
7. Occasionally the Cantharians will capture station 1 in which case you must move in and kill it immediately with the gunship.
7b. Sometimes the Cantharian carrier hangs around. You will have to kill that also.
8. If you take and hold bunker stn 1 the transports will enter the system and build the Battleship unmolested.
Then make it up as you go along
9. Once you have taken Bunker 1 it is best to dig in and defend until all the transports have arrived even if the Cantharians take Station 2, though if you are good at strafing Bunker Stns with gunships you could have a go at knocking it out.
Sometimes if I do well, I can grab the second bunker station, though I usually go for the second flak drone by building a second engineer pod and positioning it at Assembly Point A until there is a chance to sneak it in against the flak drone.
As Pallas said, you don't need the Battleship to win. First time I played the level I didn't get it and had to dig in and win the hard way. My, that way a long time ago
hope this helps