1) Yes, as a general trend. However, I've only found one substitute where the change from VHF down to HF is worth it, and thats from the Manta to the Hammerhead (even though both are pretty good fighters in themselves imo)
2) No, the trader should pay for his life. Its not out of roleplay to demand cash from them in exchange for their life only. However, you'll 99% get the "Kill me its cheaper" line off them, unless they're factionalised or the pilot values RP over making money.
Well, I wouldn't know anything about the HF/VHF question, because I mainly use factions who don't have many HFs, however, the Greyhound is a very good HF, if you can call it that, which has substantial maneuverability advantages over the Werewolf, it's VHF companion. They're both good ships, but, if you like Maneuverability, the Greyhound is the better choice.
Onto the pirating question, you should, instead, ask yourself if you are OoRP for not asking someone without cargo for money. It's not OoRP for you to ask for money, but it might be against your RP to not ask for money. Afterall, some characters have more than just money in mind, however, the other side of the fence would want money just as well.
In short, pirate them to your heart's desire. I do it, and I hope that it gets the message across that whether or not you're doing something conspicuously or not, you're still doing something.
[8:32:45 PM] Dusty Lens: Oh no, let me get that. Hello? Oh it's my grandma. She says to be roleplay.
[12:49:19 AM] Elgatodiablo: You know its nice that you have all that proof and all, Bacon... but I just don't believe you.
From experience flying the Stiletto, yes, HF are in general faster than VHF. I haven't done any real testing but I'd say they turn around nearly twice as fast in a joust. Gives you a lot of advantages, now if only they'd rebalance the unused HFs (Stiletto, Falcon & Centurion) As is stands now, their firepower is too weak to even really dent a VHF without explosives.