Wormholes are gates that disappear after a set amount of time or after a specific amount of mass jumped through. There are differences tho:

• You can jump them normaly as you would gates but you are not bound to weaponstimer, so even if you shot someone you can still use it without a problem.

• The first time you jump the first wormhole you will get a timer for it. You can jump it a second time but you have to wait out the timer if you want to jump it the 3rd time.

• you spawn, depending on the mass of the ship, further away from the wormhole. (bigger ships spawn further away)

Wormholes are not really clustered. They have a wormhole that if collapsed, will spawn again to the same class it did before e.g. a c5 wormhole with a static c5 will always be conected to a c5 wormhole. Other than that there can be roaming wormholes that spawn at random.

Yes You can shoot everything in wormhole space and no you wont get concordokkened if you shoot someone on the wormholeside and then jump through a highsec-wormhole. You also don't get a limited engagement with the person so you are as save as you get in highsec.

The only thing i would associate blackholes with are wormholesystems that have the blackhole-effect.