If I could create wormholes at will, I wouldn't traverse the wormhole with the whole ship - just the bombs would suffice.

If you can create wormholes at will, you don't need bombs. Put one end of the wormhole in the target and the other in the center of the sun.

Any guesstimates on how large the wormhole would need to be for it to be a doomsday device? Two estimates, one for a wormhole on the surface of our sun, and the other for its core. I'll try to post my results sometime later.

What about a neutron star? It's probably too exotic to consider how a wormhole would interact with a black hole.

That makes little sense. Do I assume that use of a wormhole circumvents thermodynamics? After all, the sun is in the bottom of a rather large gravity well. It's about 900 MJ/kg from the sun to earth (I think that's measured from the core). A megaton explosion is 4.184 petajoules, so if you could move 5,000 kg from the sun to the earth then it's the same amount of energy you would need to set off a megaton explosion.

I don't know how much density is in a 5,000 kg chunk of the sun.

Why waste bombs. If you can create wormholes at arbitrary locations just teleport piece of a star into a planet.

If I could position both ends arbitrarily, a better approach would be to connect the planetary core with a black hole.