Ghouls are Chaotic Evil unless the DM houserules otherwise. For friendlier undead you might want to look at ghosts. Ghosts can be any alignment, and are mostly Neutral, and are more willing to carry on a conversation. Elves typically use other elven ghosts as guards, or sources of ancient advice. They are more than willing to converse.
- Are they truly capable of elaborate communication (like a conversation), and willing to engage in some?
I would say that in this instance the answer to this would be yes, they are capable of elaborate communication provided you're able to restrain them. In the end ghouls are twisted abominations that hunger for the flesh of the living, angry at the living because they were torn from life before they felt their time was up, and while they have the ability to communicate, that doesn't mean they have the desire to do so.
- Do they have clear memories of their former lives?
I would also say that the answer to this question is yes. They have memories, and its those memories of their lives that fuels their hunger, they remember their lives, they envy the living, and it enrages them to the point of wanting to end the lives of anything alive after their death.
- Do they feel genuine emotion, and possibly regret as to their lost life?
To this I would say.. no. While emotion is not typically felt by undead, they're even less likely to feel regret. Rage and anger, are more likely to occur. This person died because of a Ghoul. A ghoul paralyzed this person, ripped out their neck with their teeth, and left them dying, and Ghoul fever caused this person to rise from the dead. To my knowledge other than raising someone from the dead as a ghoul, there's no other way to create one other than by Ghoul Fever.
A ghost is someone who had lingering feelings on the material plane which let them stay on the material after their death without becoming a resident of their deity's plane. They would feel regret because they didn't get to do whatever they wanted to do with their life. They would feel regret. A ghoul probably would not.