Maintenance for the week of April 20:
• NA megaservers for patch maintenance – April 20, 3:00AM EDT (7:00 UTC) - 12:00PM EDT (16:00 UTC)
• EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
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.