Kurzick and Luxon Armor

If I'm allied with Kurzick, can I use buy and wear Luxon armor?

Yes, you can buy luxon armor if you have more lux faction then kurz, not title wise tho

As long as you have more Luxon faction than Kurzick so you can talk to the NPCs, yes.

Yes but you'll need Luxon faction. Best way to obtain that is by getting a guest invite to a lux guild and go AB for a bit. Or you could do some Luxon quests.

you can buy and wear armor from either Luxon or Kurzick Armorers, regardless of your own "affiliation" - you simply need more current faction with whichever side you want to buy from at that time.

No not really. The luxons won't speak to you unless you have more luxon faction then kurzick faction. Kurzicks on the other hand will always speak to you even if you have more luxon faction. The only thing that's hard is getting the jade or amber (but you can buy that anway).

I'm fairly sure that the Kurzicks don't speak to you if you have more luxon faction than kurzick.. they say something along the lines "Yeah, your guild may be affiliated with us, but you've been helping the luxons.. Jog on son."

Back on topic:
What everyone else said, get some more luxon faction than kurzick and then you can craft some luxon armour.

yes im also pretty sure it works both ways, the side with the lower faction wont speak to you, so go guest AB or do some quests till you get higher lux faction then buy the armor.

Yes, it does work both ways. I've ran into this crap too many times trying to get through factions not to know this for a fact. It's one of the biggest reasons why I despise that chapter.

It's really not that difficult, you only need more of one faction than the other. So, if you have 0 (zero) Kurzick faction and 100 Luxon faction, the Luxons will talk to you. You only need a significant amount of faction (10,000) to complete the "Befriending" quests.
The only thing the OP needs to do is to dump all his Kurzick faction points (buying amber, etc.) and then get a few Luxon points - unless, of course, he needs to do the "Befriending the Luxons" quest to get to the armorer.
But, since faction is now similar to other points, it's a lot easier to get. That is, once you talk to the priest (Luxon or Kurzick) at a shrine (outside of an outpost) and get the Blessing, you gain faction every time you kill something (gain experience), much the same as getting LB/SS/Asuran/etc. points. So, it doesn't take very long to get 10,000 Luxon, just do the quests leading up to Cavalon and kill stuff.