
Originally Posted by
Heroshi
1. First off, the City-State on your character screen > Profile in-game, does this change when you pick Grand Company or what? I'm having a real hard time choosing where to start out (though it doesn't matter much, as I'll wind up being either Paladin or Warrior by the end of things, and both require at least *something* from a zone, so I'm choosing based on story reasons and just personal preference with looks.
No, starting city has no connection to which Grand Company you join (you'll see why when the time comes). You can pick a totally different Grand Company to the nation you start in. Really it's not important which one you select, as it's mostly just aesthetics which differ. Starting city is chosen by what class you start out as anyway, specifically, the location of that class's guild - because one of the first tutorial quests upon starting the game involves joining up with the guild of your starting class. At the moment, your starting nation cannot be changed later - although apparently SE are considering giving this option in the future.

Originally Posted by
Heroshi
2. Could anyone give me a rundown (as spoiler free as possible) of each zones starting story? By this I mean the 1-15/20 content until you choose a grand company and everything pretty much becomes the same.
Each city pretty much ends up with a similar flow of gameplay (there's not too much spoilers here, but there is a lot so I've spoilered it anyway:
you wake up from a dream with an Ascian on a chocobo carriage/ferry and are given a rundown on the city by a merchant, is given a starting ring depending on how you answered his question, join up with that nation's adventurer's guild, join up with the guild for your starting class/attune to the aetheryte/learn how the markets work, then sent to a nearby outpost and help out with a npc there, ultimately being sent to investigate an incident nearby which results in your first boss fight (where you also meet the Archon for your starting city for the first time, as well as seeing an Echo vision of the 'star shower' and the Mothercrystal), then sent to another outpost further out with more fetch quests before being sent to investigate a nearby ruin which results in a solo boss fight against a golem, triggering another Echo vision of the Archon in that area prior to the Calamity, whereby returning to the adventurer's guild you're rewarded with access to the Inn as well as being able to undertake guildleves.
After this, you're sent back to another outpost for more fetchquests, ultimately leading to hunting a 'man in black' who is stirring up the local beastmen, culminating in a boss fight with the local militia against a group of beastmen before then facing down the 'masked mage' and a gargoyle. After this you return to your starting nation where you meet your nation's leader for the first time and have to participate in a special event (Festival/banquet/ball) where you see an Echo vision of the Battle of Carteneau and ultimately are then chosen by your nation to represent them as their envoy to the other two nations to organize a memorial service for those lost at Carteneau, which is where you receive your airship pass - you also receive that nation's ring as well as another accessory that differs for each nation, plus an wind-up airship minion.
After meeting with the two leaders, you're then sent to Limsa regardless of your nation and are asked to investigate reports of pirate activity in your first dungeon, the Sastasha Seagrot. After completing this you're then sent to Gridania and have to likewise investigate an evil cult in the Tam-Tara Deepcroft. After this dungeon you're then sent to Ul'dah and have to hunt down ancient giants in the Copperbell Mines.
When you return to Ul'dah following the completion of Copperbell, you have to assist a hapless girl being harassed by some thugs which triggers a fun boss fight, before the Archon of your starting city shows up after another Echo vision and directs you to Vesper Bay where you join Minfilia's secret group the Path of the Twelve Scions of the Seventh Dawn and learn about the Echo, gaining the ability to use retainers. You're then teamed up with Thancred and investigate unsavory events involving the amalj'aa in Camp Drybone, ultimately leading to your first Primal battle against Ifrit.
After Ifrit is defeated this gains the notice of the Grand Companies who show up at the Waking Sands and each try to use you as a morale booster, thus any of the three you're free to join. You have to visit each city and participate in the memorial event for the Battle of Carteneau before you select one though, and even then, you're sent on a mission to protect an airship called the Tiny Bronco which involves a boss fight against some Garlean soldiers.
After all this, you officially join the Grand Company, although ironically the storyline actually doesn't continue to follow it, instead returning back to Vesper Bay. That's it in a nutshell anyway.

Originally Posted by
Heroshi
3. A rundown of each grand companies story as well. Of course, as spoiler free as possible.
Besides the first part where you actually join them, there actually isn't any real story for the Grand Companies. There are several quests you can do for them which also unlock access to the Dzamael Darkhold and Aurum Vale optional dungeons if you haven't already unlocked them, which are necessary for promotion in Grand Company rank, but they're not required as part of the actual main storyline. A third quest from your Grand Company unlocks PvP at the Wolves' Den. Really though, there is no real storyline for your Grand Company - after joining it you could easily go through the rest of the game with no further connection to them at all.

Originally Posted by
Heroshi
4. Is it possible to change company?
Yes, but only after you've attained the rank of Second Lieutenant (currently the highest attainable rank in the Grand Companies) - this requires you to complete the first two Grand Company hunting logs and also the two dungeon quests they give.

Originally Posted by
Heroshi
5. Does the gear from them even matter much in the long run?
Grand Company gear is very useful, but ultimately you will receive better gear that makes GC equipment redundant (GC gear currently is just 'green' gear with it's highest item level at 55 - you get gear far better than that later on). Still, until end game GC gear is still well worth getting (incidentally, if you've played Lightning Returns ~ FFXIII yet, ARR's level 50/iLevel 55 Grand Company swords for GLA and PLD show up in that game, ala the Gridanian Longsword, Ul'dahn Katzbalger and Lominsan Cutlass).