Halibut mainline, topshot, leader?

Pretty much mooching style. One mono line with a hook crimped on. Then another piece of mono crimped onto that hook's loop with another hook crimped on the other end of that second piece.

The main difference between the J style hook and a circle is that with a J you can set the hook and a circle you're waiting for the halibut to take the bait and set the hook himself.

I prefer to use circle hooks where you have to fish barbless for halibut - like out of Freshwater Bay.  Make sure they are sharp - seems a lot of those big hooks are dull out of the package.
If you are at Neah Bay then barbed J-hooks are fine - especially if you are like me, and have a tendency to set the hook as soon as the rod tip twitches.