1. If you're referring to the artwork used for the aliens of Thaddeus 10: Galactic Renegade, I stole practically all of it merely because I was a dumb 12-year-old, so, sadly, no. The only reason it's still up merely because of the fact I rather ignore all of my cringy BTFF work back in mid-2016.
2. I vaguely remember the Jessica character you're referring to, but if it has artwork, it's most likely stolen as well.
3. There's no page of Jessica. I didn't get that far into the series for her to appear.
However, Thaddeus (though only his name and obsession with purple) has technically made a reappearance in one of my recent BTFF projects, a series called Ezekiel Elix: Power in Courage, as a villainous foe, starting from Episode 10. Though that series was cancelled a while ago for not liking how it was turning out, you can read its remake I'm currently working on, Ezekiel Elix: Peculiar Institute's Crimefighter. I plan on possibly taking a few forgotten elements of T10:GR, such as reinventing Thaddeus, and incooperating it into EEPIC's remake.
Hey, WTB. I heard you were going through some stuff. I read your essay on your wiki (the one you linked to on your userpage). I just want you to know that I'm sorry life's been tough on you, but it will get better eventually. If you ever need someone to talk to, I'm always on the wiki and Discord.