The key word is meddling. It only counts as meddling if you get caught. Just like the rest of the oath.
House Jerbiton has always had problems with that clause of the oath. Much like how Merinita has had problems with the precise definition of "molestation" vis a vis the fey.
First. The Jerbs are more than meddlers. They appreciate beauty, scholarship, and the noble world. The intent of this clause of the oath is to prevent having the Pope (or God) go "enough!" and call down a crusade. The ultimate problem here is that if magi are caught giving magical aid to one side, the other side will cause all sorts of problems.
This also varies significantly by tribunal. Most tribunals (according to ArM5 lore) are OK with charged magic items being sold through sufficient cut-outs, and political aid being given to favoured sides. Beyond that, there is a pragmatic realization that, just like the Merinita, that dealing with mundanes is an annoying job and someone has to do it.
On the other hand, meddling is an excellent pretext for charges at Tribunal, and so it is a very careful minefield indeed that politically motivated Jerbiton tread. The rest, dedicated to the Fine and Liberal arts have no problems.
At the end of the day, this is one of the most politicised areas of the oath. The young jerbs, incensed at the fall of Constantinople routinely flout it, and the older ones are too occupied with living the beautiful life to care. The fact that the Jerbitons who are into politics are good at politics means that anyone who chooses to play... a game of thrones... already has significant allies within the order (bonisagus, tremere, tytalus, to name a few) to fend off the trivial assaults.
Again, it's only meddling if a) you get caught, and b) your accusers live to accuse you. If you don't endanger the order through the view of your local tribunal you haven't done anything wrong.
Being a merchant is excellent. Your magic provides mobility, keeps your goods safe, and your person ... safe. If you avoid using it against the people who matter, no one will care what happens to one random group of bandits or another. If you don't flaunt the fact that you can carry your entire year's worth of goods as a small marble block on your belt... no one will care. Beyond that, if you take some of the duties of the mercere on your head and serve as an intermediary for mundane goods to the other covenants in your tribunal, people will consider you a valuable effort.
The Jerbiton who meddle tread a fine line, but consider the adage: "Why dost treason never prosper? If it prospers, none dare call it treason." Your character concept is absolutely suitable. Don't get caught selling magic items to the mundanes, and don't get caught helping various feudal lords squabble. Or, if you do, make sure your value to your tribunal is high enough that they simply don't care. Also, remember, that if you do get caught, you've got plenty of shiny shiny things for the tribunal to fine you. It's not like they'll march you if you can bribe enough of the voters.
Does your concept work?
Maybe. What are your goals? How are you living a beautiful life? Why are you travelling? What is the rest of your troupe engaged in? What kind of stories are you planning to tell?
Ars is known for providing all sorts of stories. Be careful that you make a character with motivations, and a stance on all of your house's major issues. Make sure you make a character compatible with the rest of your troupe and at the timescale the game is played at. And make sure to figure out how to keep your lab with you, or you'll be missing out on a huge part of the game.
How can I be the shadow controller of a merchant empire?
Rather more easily than being an actual merchant. The trick here is not absolute secrecy. The trick is to not get caught. In ArM5 there is a lovely set of rules for Agents that I'm sure can be backported. In a general sense, you can set up your own personal, trusted, and completely mind::cough::ed merchants with very subtle kit, charged items designed to give them an edge in transport, defence, and the ability to alert their chain of command if necessary.
From a trivial perspective, knowing the market prices across Europe, as transmitted to a trusted grog (we don't want to be creating charged CrMe items that can penetrate your own parma now, do we?) is an incredible boon. City and Guild (again ArM5, but nothing is edition specific) has an excellent discussion on the use of magic as a merchant. Functionally, using it as part of your command and control network, especially if the majority of your people don't know that they're working for a magus, provides incredible flexibility and power over people who don't have it. So long as your enemies never learn that you're doing this magic-enabled trading, and you have sufficiently adequate panic buttons to ensure that anyone who does learn doesn't go blabbing it about, and you have the excellent basis for a character, stories, and a way of bringing income to your covenant.
