I still don't fully understand the merchant rules, but I'm willing to figure them out. So go ahead and start making actions, Ardas.
Short Version1. Buy goods in Port Alpha. Decide what good you are going to buy and then consult the Wiki page for the province and the Merchant Adventures spreadsheet (there is a permanent link to it on the Resources page in the Wiki). The
Base Price of the resource is the price you should start from.
1a. Roll a d6 to determine the number of 'increments' to adjust the base price by. On a roll of 3 or 4, make no random adjustment. Every point
less than 3, decrease by 1 increment. Every point
above 4, increase by 1 increment. Give a bonus or penalty of +/- 1 to this roll if the merchant rolled a 5 or 2 on their travel roll (see point 2).
1b. Now apply the province modifiers. If a resource is produced in the province, reduce by 3 increments. If it is a staple, industrial or luxury good, adjust according to the modifiers on the Province page. If the resource falls into multiple categories, apply all relevant modifiers (they stack). If the resource is illegal in the province, increase by 3 increments.
1c. If the province is in a state of war or siege, or is still recovering from one, increase the value of staples and military goods by 2 increments and decrease the value of luxury goods by 3 increments.
1d. When you have arrived at the final increment total, multiply this by the 'increments' value from the spreadsheet and apply it to the base value. This is the final price at which the good may be bought. Up to 6 units of the good may be bought from a province that produces that good. Goods not produced by the province are available in lesser amounts (see the OP for details).
2. Having purchased your goods, travel to either Port Beta or Market Gamma by ship or caravan respectively. Roll 1d6 once to determine any difficulties experienced during travel.
2a. On a 3-4, the journey goes as normal. On a 5+ the journey goes particularly well and the merchant arrives in time to get the best deals: add a +1/-1 bonus to any sales or purchase rolls made at the next port (whichever would be more favourable). On a 2 the journey goes poorly and the merchant arrives late, receiving a -1/+1 to any sales or purchase rolls at the next port (whichever would be
less favourable). On a 1- the ship is attacked by pirates (if any pirates are in the region) or caught in a storm (see 2c). The same events apply to caravans, except that the caravans would be attacked by bandits instead of pirates.
2b. Every bandit regiment or pirate ship in a province decreases the travel roll by 1. Travelling in a convoy increases the travel roll by 1 but merchants will not receive the competition bonus for a 5+. On land, roads improve travel rolls by 1.
2c. If caravans or ships are caught in a storm, each caravan/ship must be rolled for separately. On a 1, the caravan or ship is destroyed. On a 2, ships but not caravans are destroyed. On a 3 or better, the vessel survives with all cargo intact. Any survivors reach the port/market late and suffer the competition penalty for a travel roll of 2. Due to a strange quirk of the gods, ships can only get hit by pirates
or a storm on the same journey.
3. Having arrived in Port Beta, sell the goods. Repeat the same process as for step 1, but with the province page for Port Beta. If the merchant is lucky and has planned his journey well, he should make a profit! Be aware that most provinces will charge a Sales Tax as a percentage of whatever he takes from his eventual sale. He may then also wish to purchase more goods, and the cycle rinses and repeats.
A merchant "kingdom" would be a good idea, especially if it combined with a Trade Guild. Also, there is the nefarious 'Storm Coast Guild', but only players who deliberately start out as merchants get their credit scrip and eventually they will get demands from the Guild which they will either have to accede to (and get a higher credit rating) or leave the Guild and strike out on their own.