The first thing to remember about feudalism is: there's no such thing as feudalism.

It's basically just warlordism. I suppose you could call it an oath-based society, where people take oaths of loyalty to an individual (and, technically, to his or her family). They promise to carry out services in return for protection and reward in the forms of both moveable and fixed property. "Property" here includes currency, valuables, livestock, slaves and land; "services" include working on fields, paying taxes, building and maintaining infrastructure, and turning out to fight. The classic "pyramid" structure with a King on top, nobles etc. underneath him, knights and sergeants-at-arms below them and the peasantry on the bottom is, while wildly unrealistic, a decent model to assume for game purposes.
Given that Oolite is a trading game it would probably be best, and more interesting, to assume a late (15th/16th century) feudal setup rather than an early one, where currency and non-noble (but very wealthy) merchants are mucking up the neat picture. You have military families subsisting on ancient glory and (rapidly fading) military usefulness, being simultaneously fawned over and undermined by the rising bourgeouis class. See if you can get hold of a copy of
Jabberwocky: it's a great guide to that sort of period.
Noble families would be contemptuous of mere trade as an avenue to wealth: riches and power should be achieved by force of arms. However they would be extremely jealous of, and tempted by, the enormous amounts of cold hard cash that trade makes possible.
Noble Houses could maybe have their own family convoys, with a Python or a Boa or Anaconda protected by a squad of outriders against both pirates and raiding parties from other noble houses. There would be royal convoys too, which presumably would be the richest and best-guarded. Nobles might occasionally try to rob these, if they were feeling rebellious, but generally they would probably confine their pilferings to lone traders and other Houses. They might sometimes encourage or even pay the occasional freebooter to take a pot at one of their rivals, though, and they'd be admirers of military skill.
A particularly powerful noble House, or perhaps a major religious order, might even set up its own trading station: or maybe (if combined with Thargoid's Planetfall OXP) players could try landing on the planet for a bit of direct trade. This would probably be frowned upon by the Crown, who would try to maintain a bottleneck grip on trade for taxation purposes (because actually getting one's overmighty subjects to fork over what they owe you is more of an art than a science). Bypassing the Royal trade centre – presumably the main station – should give better deals, though.