Could someone explain episode 66? Was Catherine de Bough/Ricky giving Charlotte lots of work for the whole Caroline saga? And how did Ricky know about Lizzie blackmailing him?
He knew because she phoned him to threat him. The excess of work may have been because of this, but more likely, he was just being ambitious and overworking her.
Why is Fitz so popular among fans, and among other characters in-universe for that matter? There might be some charm in him, but the writing for his character is a lot different from the original novel. They did not want him to be a love interest for the ladies, so they made him a gay. The diversity is this show's thing, and it's usually awesome, but Colonel Fitzwilliam's flirting with Elizabeth was very important for the plot. His matchmaking schemes here are out of the original character and really meddlesome. Gigi being a Shipper on Deck isn't the greatest thing in the webseries aither, but she has other engaging qualities which explains her popularity with fans. In the care package episode, Fitz was a little too happy and too easy-going, but ultimately, he did not even remember Jane's name. Humour is very subjective, but his ever popular "charisma of an agoraphobic lobster" can come off as trying a little too much, verging on Dude, Not Funny! as he was talking about his best friend. So why is he such a dear favourite?
The thing is, he sticks with Darcy despite him being what he calls "an agoraphobic lobster", likes both Lizzie and Darcy, has a nice sense of humor, and actually treats everyone pretty well. He is also quite self-confident and eccentric. I like him too, but I think that you are right to point out that the joke was harsh. I think he and Darcy must be Vitriolic Best Buds, although Darcy has a milder taste in joke (he simply impersonated Fitz).
Episode 70 "New Jane" has Jane asking Lizzie what's she going to do with her life after finishing her degree, implying she should find a job and move out quite soon and even hinting that she should have accepted Rickie's job offer. How can she be asking that question when she herself had been still living with her parents for quite a long time even after she had finished her degree?
She probably said it because she wants her sister to have something she thinks is the best for her, the sort of life she just started getting a taste of and likes.
So... Darcy can track the location of anyone who downloads Domino. Is this either ethical or legal?
It may not seem morally ethical, but it's likely legal as IP addresses and phone locations can be tracked down due to server logs and apps requiring location permissions before downloading. Darcy can take a look at the logs of recent Domino downloads and go from there.
Was is ever explained why the Bennets didn't call the police on Wickham? The tape might have been recorded consensually, but using it for money making scheme screams "sexual abuse" and perhaps it violates other laws for protecting a person's rights. The police could find Wickham just fine and deal with him as he deserved. Of course that would steer Darcy from being a Big Damn Hero rescuer but did they even consider calling the police?
Maybe Wickham could've still released the sex tape, especially if they went to the police. He was going to jail for threatening to release the tape, why not go ahead and release it anyway.
Plus, the laws surrounding revenge porn in California either weren't in place or were relatively new (I cannot find an exact date for the law), so there may have been nothing the police could have done. It's also implied in series that the Bennets can't afford to go to court over this issue.
No idea what the actual laws are, but according to the novelization, a lawyer told them that they couldn't do anything until the tape was actually released.