freighters haul freight, tankers haul fuel, shuttles are worthless and everything else shoots stuff & carries loot.
Everything but the latter isn't needed.
As for weapons, higher DPS = better, lower flux cost = more useable. If you have a weapon that you can keep using comfortably but doesn't put out enough damage, you can upgrade to one with higher DPS and higher flux.
RE: Transponder, best to leave it until you're more used to the game.
Best ships for trading are any ship with a large enough hold to carry enough goods to fulfill a contract that you can afford to fill (if someone charters you to fulfill a 3000 gun demand, there's no need to look for a ship that can carry 3000 guns if you can't afford to buy 3000 guns. Which is why earlier I said no to worry about freighters, unless you find yourself in explicit need of one)
When equipping ships; kinetic works well against shields, frag works well against broken armor and high explosive works well against something with armor up.
If a ship has shields up it's taking 0 damage anyway and most ships you'll ever face are basically dead by the time you've blown through their armor anyway so, equip flexible and cheap kinetic that's strong enough that you don't find yourself struggling to break through shields, and the rest should be your "hitting" guns, IE mostly flux-inefficient explosive guns (that you won't use unless you can land shots on an unshielded target) or some extremely flux-efficient frag guns that you can fire without worry about their firing cost (flak, Vulcans) to make the explosives shots that you do land deadlier than they would be on their own.
TLDR; if you struggle against shields, more kinetic. If you struggle to kill something after its shields are gone, more explosive. If you have a bunch of explosive guns and can land a good round of hits in but then don't have enough energy to keep dealing damage before they gets their shields back up, replace one or two of either your high-cost or low-damage explosives with a cheap frag gun.
If you want a good starter ship, you can work towards a lasher, put two machineguns on it (dual or standard, doesn't matter), fill the rest with a mix of explosives and frag that you switch around till you get comfortable with your output. If you're going out and picking fights in the game itself and not doing all the tweaking in the simulator, just be sure to be quick to flee before your armor is gone (the green picture of your ship in the corner) because if the enemy has anything to shoot at your missiles with, once your armor is gone chances are what they're shooting your missiles down with will do serious damage