It costs about 2k gold to get a clan charter from an NPC, theres no size minimum for starting one but you will need a few people to help you grind mobs to get the 2k gold in the first place since most gold comes from selling loot.

For another 2k or so (I can't remember) you can buy a Clan Shard, which is a small blue rock that allows anyone with General or Higher standing to claim clan stones, this works by simply walking near the stone and double clicking the Clan Shard, it took the beta server about 4 hours to figure this out despite being given pretty direct instructions in the beta forum. The person who claims that town becomes the Mayor, currently you can't remove or change mayors because they haven't fixed it yet, what good the mayor is or does I don't know as we never had enough time to build up a town to actually find out.

Now you have to grind resources to build little building templates that you use to build basic structures for your clan city, this requires a skill that costs a ton of gold and each template requires about 300 gold and about 5-10 pieces of wood and has a 66% chance fail rate, each template weighs a damn lot, but you only need to drag it to a bank and then have a guildmember pull it out of a wilderness bank by your city and relay the crap until you use it to facilitate building something.