Got an example stat finished for France.
https://docs.google.com/spreadsheet/ccc?key=0AvV4Kmm-PsYUdGk5LVJ3blFCdjg3dDg0Tm1CWmZCcWc&usp=sharing
Most of the stats should be self-explanatory. I got rid of Resources, infrastructure is no longer tracked on the map (and is based on the Civil Technology), and revised country income to be
[(Manpower*Infrastructure*Manufacturing)*Tax Rate*Stability]-(Infrastructure*$100,000)+(Market Worth*Tariff)
Military maintenance isn't factored in because its, err, high. The numbers on the sheet is actually wrong because Military Tech increases the cost by MT/5. It says $700,000 in the stats, but it is actually $4 million. That isn't shabby really unless France decides it wants to launch a major military campaign and throw everything it has against someone. Then the cost rises to $20 million, but that's an extreme example.
Manufacturing replaced Resources. Infrastructure costs about a million per level to rise (not too shabby, given it increases France's revenue by nearly the same amount immediately) and is the upper limit to the manufacturing stat, which costs a full $10 million a level (which is great, given this immediately boosts revenue by $12 million in France's case).
However, merchants will take care of manufacturing if you let them.
Originally, for the trade system, I was going to bum off EU3 but decided I'll just use the Import/Export system I was going to use a few months ago. Each country has a Market Value and Market Shares. Market Value is the amount of money one could make from that market, while market shares, like the shares you're thinking of, is the cut you can get from that trade.
Market shares do
not work like MPIV Influence. The amount of shares per market is a hard value and the only way to lose or gain shares is by trading shares, nationalizing shares (giving your own merchants the shares of another country's merchants), blockades which gradually loosens a country's hold in another market, and a few other ways I'm sure players will think of.
To increase your Market Value, you have to Export, which means you need to help your Merchants gain shares in foreign markets. As your shares in foreign countries increases, so do your exports, which increases your market value.
On the other hand, having foreigners in your markets increases imports, which decreases market value. If your trade balance is positive, your market value goes up and if negative, it goes down.
You could try to nationalize your entire market so only your own merchants are there, but that has its downsides. Your tariff income won't increase, because you would have no imports and exports, and you would be missing our on the potentially lucrative market share swapping market.
Selling shares is a good way to raise money. If you just put "put X shares in X market up for sale", NPC merchants will buy up the shares at market value (50% of the amount of money the share would bring in), putting money in your treasury.
But for the most part, if you're thinking long term and weighing the costs of controlling $8 million of your own market or exporting $8 million, exporting is usually the better call.
The only thing that "increases" the amount of shares on a market is piracy and privateering. Pirates are based out of countries with low stability/countries that turn a blind eye on it and privateering is when you pay money to commission privateers.
The difference is this. Pirates out of Great Britain would leech off some money from the French market, which would count as an export and therefore increases Great Britain's market value. Merchants in Great Britain, if stability is low enough, will use some of their earning to create more pirates, and the process continues.
Privateers out of Great Britain do the same thing, except they don't create more pirates. Privateers also limit their activities just to countries approved by their commission. If GB only targets France, Spain doesn't have to worry about British privateers.
Pirates aren't so easy to control, and in GB's case, the pirates won't just go after France, but Sweden, Norway, Spain, and other countries as well.
Countries can't nationalize pirate/privateer shares in their market like they can other shares, because pirate/privateer shares are phantom shares. There are two ways to deal with pirates. The first way is by ordering Naval Power to protect the sea lanes, which makes plundering said sea lanes less attractive to the pirates, who will go after something else. The second way to deal with pirates is more expensive and involved going to war with the pirate stronghold country and purging it of the pirate strongholds.
Pirates are also created from naval casualties at sea.
Privateers, unlike pirates, won't shift targets based on sea lanes being patrolled. It just means that privateers are less likely to be effective.
If stability in a country is particularly low, pirates might just target their own country, which increases the domestic trade value (neither an import or export) and lowers domestic trade value and imports. This can actually be useful sometimes because decreased imports means a better trade balance, but it makes others wary about buying trade shares in your country.