Side note, but I think T8 Shoulders/Gloves might be "best" in that the best 2T8/2T9+1 offset piece is probably [Leggings of the Awakening].

I got the [Stormrage Crown], and I am almost at enough badges to get my first t9 piece.

I know I should get the chest, but with the ony helm which other slot should I go for? I was thinking gloves but I also just got [Handwraps of the Lifeless Touch].

For T8 I have chest/leg/helm/gloves.

I could likely get the t8 shoulders next time they drop, but I want to be sure it is worth the dkp before I do.

In case of doubt, buy the T9 shoulders after the chest, because they have crit rating, and that leaves you more room to shuffle with hit and haste in other slots.

On 2pc T9, is the i232 worth going to asap? I'm currently sitting on 94 Triumph and do not see any successful 25 man runs in the near future. Should I upgrade from my T8.5 to the 232 T9 helm chest or keep being patient and wait for the possible winning of a trophy drop?

I would wait. You can always get lucky and win a trophy from the tribute chest after clearing 10 man heroic.

So, I'm able to pick up 4pc t9 ilvl 245, but is it worth it to break 2pc t8.5 bonus?

this has been discussed before: 4x T9 comes into discussion only if you are able to get ilvl 258 versions of it (ToC 25 Heroic), and even then you might wanna make some calculations. Untill then, 2x T8 and 2x T9 is better

I still have 2T8 as better even with full T9.258 against a single target.

Two important points, also:
1) Twins has a lot of movement and Anub has a lot of AoE, and both of these weaken 2T8 significantly--you'll be better off with the stat upgrades. But, by the time you're looting 258 tokens in the first place, you're done with ToC progression and gearing for Icecrown, so we probably shouldn't consider specific ToC fights for this purpose.
2) Even if T9.258 is slightly better than T8, it's hard to justify looting them over other raid members, given their now-apparent scarcity.

With 5 Hurricane aoe targets, is it worth keeping Moonfire up on one or more targets and Typhooning between for better NG uptime or should I just spam Hurricane?

Highest damage per execute time (DPET) for five targets is Starfall > Typhoon > Hurricane.

Hurricane's DPET is nearly twice as high as a five-tick MF (Gale Winds, No IMF, No MF DoT crits). You won't get much benefit from the Moonfire Idol (neither Typhoon nor Hurricane benefit from Vengeance). If you don't have Gale Winds, and you do have IMF and critting MF DoTs, the gap is smaller. I still don't think its worth a MF cast (or 5 MF casts against different targets), unless the targets are going to live 20 seconds or more, and you might lose some of the Hurricane effect (you have to move, targets move out of the AoE, pushback danger, ...).

At even a low crit rate of 35%, Typhoon (5-target) is 88% likely to give you NG. That means Typhoon is very useful as you can cast Typhoon+Hurricane in less time than it takes to cast Hurricane alone. Moonfire increases your NG probability by a small amount, but not by enough to justify the cast.

If there are five targets clustered around a tank, Starfall will probably give you 12 NG opportunities per second, which means you are over 99% likely to have NG by the time you cast Hurricane.

I assumed that Hurricane crits would proc NG for you. With fifteen Hurricane hits during the last two seconds of the previous Hurricane, your second Hurricane would almost certainly have NG. However, I'm looking at a log and seeing Hurricane crits without NG procs (Starfall and Typhoon crits are showing NG).

If you end Hurricane without NG, using MF (tab-target between casts) to get NG may be your highest personal choice for DPS. If you aren't the only caster AoE, and you don't have Ebon Plague, Wrath might give better raid DPS (E&M debuf).

I suppose in some situations the attack-speed debuff from Hurricane might be more important than some personal DPS.