Can haz questions?

[Dogempire]

Do you know where I can claim a white devil mount? I can't find any information regarding where to use the key.

[AskaRay]

Do you know where I can claim a white devil mount? I can't find any information regarding where to use the key.

If that's the new one from the Mog Station. Click on "Your Account", then hit "Enter Item Code". That should let you redeem the mount.

[Niwashi]

1. How much will it cost to buy a housing plot? I'm not really going to be picky, I just want a place to call home and maybe afk in. I am in the Excalibur server at the moment.

This wiki lists the price ranges they start at. Theoretically, they then drop in price over time if they stay unpurchased long enough, but on larger servers especially, they tend to get snatched up before that can happen (especially the small ones).
Besides the high prices, though, there's the issue of whether you can even find a plot available to purchase. There's a severe shortage of them, especially for the more highly populated servers.

2. I'm a level 14 arcanist who might want to start making money soon, but anyways, any suggestions on making some decent money? I don't mind if you just give me an option that I can do later down the road.

People have already mentioned that gathering and crafting are big money makers. You will need to advance your arcanist (or another battle class) a few more levels before that becomes feasible, though. The level 17 main story quest "Scions of the Seventh Dawn" unlocks retainers, NPC assistants who do various things for you, such as storing extra items and managing sales of items to other players through the MarketBoard. You'll want their storage before getting very far into crafting and gathering, and can only make money from it once they're available to sell your items, so stick with the main storyline at least that far before deciding if you want to take some time out to work on crafting.

3. How viable is arcanist as a tank or as a solo character? I prefer soloing dungeons since I feel like it makes stories much more awesome (I feel like it sort of takes away from the overall story if you need 7 other random people to fight the main antagonist, but that's just me).

Arcanist isn't a tank, and nor are either of the jobs it can upgrade to at level 30. It does however have a tank pet (Topaz Carbuncle as ACN, or Titan-egi as SMN), plus some healing abilities on a damage dealer class, making it the most well-rounded, and so one of the strongest in the game at soloing content.

While you can go back and try soloing dungeons once you over-level them a bit, it's not going to be very feasible for your initial run, at least not most of the time. You might be able to do that for some of the optional dungeons, but most appear within the main storyline, so you're going to want to do that initial story run when you're on level (or near to it) in order to continue through the next part of the story on-level. On-level, they're not really solo-able.

Do you know where I can claim a white devil mount? I can't find any information regarding where to use the key.

Use the item to add it to the list under "Mount Guide". Use it from the Mount Guide to mount or dismount. Before being able to mount, though, you'll also have to unlock the mount system. Once you join a Grand Company (level 20 in the Main Scenario quest line), do the My Little Chocobo quest at the GC headquarters. It both gives you a chocobo mount and unlocks the mount system in general, so you can also use any other mounts you have.