Maintenance for the week of February 9:
• NA megaservers for maintenance – February 9, 4:00AM EST (9:00 UTC) - 12:00PM EST (17:00 UTC)
• EU megaservers for maintenance – February 9, 9:00 UTC (4:00AM EST) - 17:00 UTC (12:00PM EST)
Guilds can be cross faction, however when the guild is created you still need to designate a main faction and while I am not sure entirely what this choice dictates, I do believe that it affects claiming resources in pvp but this is speculation as I haven't tested it. Also, while you can have people from other alliances in your guild it will still not allow to group with them in dungeons or pvp.