First come first serve when it comes to issues with buying stuff from the caravans. You aren't in a food crisis yet though. typically 4 food feeds 1 dwarf for 1 season.
Your fortress has
1 Mule Meat
7 Plump Helmet
8 Turtle
This is enough for you to last two seasons with no problems farming nothing at your current population. You can reject further population as well, preventing a swelling of population eating your food.
(Edit 1: Okay, a little definition of the trade as it will be applied. Hauling goods is going to cost 2 currency. That means every individual object that is required to be hauled will cost you 2 currency (for trade between fortresses or tacked onto the value of objects that are up on the surface and therefore available for buying.)
When you provide an object for trade, the value of that object is deposited in your "bank" as it gets delivered to the "Trade Zone". There is no extra tacked on this, since it gets added on in other places. All these "Extra" costs are to offset the brutal negotiation of merchants plus being able to supply "credit" eventually, where I can allow people to buy stuff with objects currently in their fortress rather then already deposited items. Right now, there is no "central bank" of extra stored value to provide loans against undeposited items to, meaning the extra value I have is limited to 300 ¤. As such, I will only allow a credit of 60 to each fortress for this particular go around.
Trading with Merchants is limited to the value of goods already deposited to the trader group and credit limit. Trading with other fortresses and the traders isn't so limited. As soon as you get the proper amount of currency, the trade can be issued. I view certain transfers as high priority. Food and drink is high priority, and I will unassign jobs to a dwarf to get that hauling done quickly. Seeds are moderate priority, and will be transferred before things like wood and ore. Basic survival tasks for the trader group, such as getting the standard defenses up, take priority over transfer of non-critical trades. This is why the wood hasn't been transferred yet.
The Currency as deposited by the end of the season is updated and displayed on page 1. That lets you know what you can buy. For example, Martinelli's has 1¤, MirroredAbby has 130¤, and Lamid Beravuz has 534¤. This doesn't reflect actual wealth. The Purple Cap has 42 Stone Crafts, and from my rough count it will be on par of Lamid Beravuz's wealth, if not top it when things are deposited.
On to the next step, who gets priority of deposeted items.
It goes in a circle of those who have goods for offer. Lamid Beravuz had materials when I was ready to do a pickup, so they dropped goods. The Purple Cap didn't have any at that time. Now both Lamid Beravuz and The Purple Cap have goods for offering, so The Purple Cap gets the next deposit, and then Lamid Beravuz. Right now with the limited availability of traders to trade (they are working on the Aqueduct and basic defense) only 18 or so goods will be picked up in each round. As the trader population grows, so will the ability to collect large amounts of goods.
So, to recap, Current value everyone has available to trade:
Martinelli's:
¤: 1
MirroredAbbey:
¤: 130 + 60 Credit (Your crown provides collateral)
The Purple Cap:
¤: 1 + 60 Credit (Plenty of offered trade goods)
Crashthunders The Doom of Trees:
¤: 0
Lamid Beravuz:
¤: 534 + 60 Credit (Plenty of offered trade goods)
Unnamed Group:
¤: 0
[ April 16, 2008: Message edited by: Kogan Loloklam ]