Questions :
1. How to obtain a Guild Stone?
2. The quest of guild.
3. How does guild exp system work?
4. What are the ranking system in the guild for?
5. Perceptors? What's that?
6. Attack and defend of Perceptors.
7. Advantages of having Guild House.
8. How many guilds are there currently now?
9. Guild lvls 

Answers:
1. How to obtain a Guild Stone?
The Guild Stone is dropped from EVERY creature with a very low %. The ones that have a high % of dropping them are Gobbal Warchiefs. Your best bet are the the warchiefs from the gobbal dungeon.

2. The quest of guild.
After you gained the Guild Stone you need 8 (not in guild players including you) to do the quest. Till now I have none telling me where to get the quest. Please wait I will update this as fast as I can.

3. How does guild exp system work?
The leader of the guild can put an % next to your name. From 0 to 100.
Example: He puts 50. Meaning that your every painfull and excrutiating fight, 50% of exp will be conducted to the guild. Reasons? To lvl up the guild ofcourse.

4. What are the ranking system in the guild for?
From what I know there are 4. Leader, Officer, Defender and on approval.
Leader : Like hell I'm going to explain that.
Officer : Able to kick/invite if the Leader enable the option.
Defender : Protects the guild. See Q6.
On approval : Just joined members. Can't do anything besides lvl. Let the Defenders pick on them XD.

5. Perceptors? What's that?
Perceptors are human/horse creatures. Also known as Centaurs. Guilds use them to be a tax/minerals/drops taker in a map.
Depending on the Guild's lvl and the Perceptor's strenght it can Tax every sold item (From merchant mode player or npc), gain an % for every job work like woodcutting (every 200 woods that's being cut he gains 20) and % of items drops from the slain monsters.

6. Attack and defend of Perceptors.
The fun part of being in the guild. Placed Perceptors in the map CAN be attacked by either with or without guild players.
Perceptor can have up to 8 companions summoned from his guild.
Meaning 9 (defenders) vs 8 (attackers) maxed.