1 - Glamours unlock from a quick quest in Vesper Bay at level 15. Have you noticed the Glamour Dresser in the inn rooms? If you have Glamour Crystals (crafted, bought with CG seals, or bought on the Market Board) you can put a piece of equipment into the dresser. That piece of equipment can then be used as a skin. The dresser lets you set up glamour sets that can then be applied any time you're in a major city.

2 - Doesn't matter. The Grand Company/Free Company thing doesn't matter in the slightest. You can join any FC regardless of which GC you are affiliated with. The only real difference is the location of the vendors.

3 - No limit. If you want to level every single class, go for it.

4 - You have to pick it up from the retainer. It's the second option on the retainer list.

5 - Hosing is a weird thing at the moment. You can buy a house but there are no direct gameplay benefits, outside of having a personal garden (if you're into that.) No extra storage or buffs from having a house.

Houses are not instanced, meaning there are a limited number of them in the game. The odds of being able to buy one for yourself at this point are fairly low. You can buy apartments and/or personal rooms in a FC house though. They're smaller and have no yards, but they're not limited like houses are. Apartments also have communal chocobo stables.

6 - If you try logging in a from a different IP it'll do a security thing and make you change your password. IIRC this can be avoided by using the one-time password securtiy thing though.