Okay - what about this, then:
Trader-freight: traditional traders. Anything bigger than a Cobra III gets escorts. Escort number and class varies depending on system danger levels
Trader-courier: carries packages and/or passengers, sunskims a lot. Not a pirate target. Uncommon. Mostly low-capacity ships like the Adder, Asp or FDL, but an occasional Anaconda or Boa II liner sounds good too.
Trader-smuggler: carries high amounts of contraband. Almost always has fuel injectors and runs rather than fights. Offender status. Uncommon. Mostly small fast ships.
Trader-opportunist: most of the time acts like a normal trader, but starts with a little bit of spare hold space. Will scoop loose cargo and will attack lone ships. Rare. Similar ships to the standard traders.
Hunter-light: non-witchspace capable hunters. Often found on patrol, most common in medium-danger systems alone or in small packs. Stays in home system.
Hunter-medium: witchspace-capable hunters. Will launch from a safe system, make a short jump to a nearby medium or dangerous system, patrol, then return to the safe system.
Hunter-heavy: heavy fighters. Appear with several medium and light hunter escorts. Will launch from a safe or medium system, make a jump to a dangerous system, patrol, then return.
Pirate-*-fighter: muscle for a pirate freighter. Fighters whose group no longer contains a freighter will return to base and/or join nearby freighter-led groups. Light, medium and heavy versions, similar in power to the escort or hunter classes.
Pirate-interceptor: patrols spacelanes, attacking hunters and police. Fugitive rating. Rare outside of dangerous systems.
Pirate-independent: lone or small group pirates. Will not team up with freighters.
Pirate-*-freighter: pirate group leader. Grouped with several pirate fighters. Heavier sorts rarer with bigger fighter groups. Usually only in dangerous systems; may occasionally raid nearby safe systems. Light: Cobra III with LCB, Medium: Python, Heavy: Boa.
Escort-light: traditional light escort fighter. Default escort class for most freighters.
Escort-medium: tougher escort fighter, with beam lasers. Default escort for Anaconda and for freighters in more dangerous systems.
Escort-heavy: heavy escort fighter. Freighters entering the most dangerous systems may have one or two of these in addition to their normal escorts. Asps, Cobra IIIs, iron-ass Geckos...
PDF table of possible role weights to give a better idea of the sort of ships I envisage at each level.