GvG is going well, for the most part. I will talk about a few things. Once a guild takes a province, there is a cooldown time, where no other guild can attack for a set amount of time, not sure of time, but it may be something like 6-8 hours. Anyway, once this cooldown is over, you can then try, and take over there provinces. You lay a Siege army in there province, and all guild members can take part in wiping the defenders out. The How-To explains a lot on the fundamentals, so I will not go into that much.
As to if you go over the Iron Age into the EMA, will you not be able to play those maps anymore? This is a yes, you can still play, it does not depend on what age the player is in, it depends on the army you bring to the field. Iron Age maps only allow Iron Age units to play in them. So if you are in PE< you will have to build Iron Age barracks, and take Iron Age units into the battles to be able to participate.
GvG is hard without cooperation from your guild, defending a province takes a lot, you can place up to 8 defending armies into your guild province once someone in your guild takes it, and when someone attacks your province, they must attack 10 times per army to defeat the army, which makes 80 attacks to take a province with a full 8 armies in defense. Yes, that is a lot of attacking, but if your guild takes part, that cuts down a lot of the effort on the guild as a whole. 10-15 people attacking that province above would take around an hour, or two to take it over.