May ask 2, 6, and 12 from the fanfic asks, please?
2. What fanfic do you wish you got more response on?
The Horizon Line. I love Horizon, I think it's one of the best things I've written, but (by my standards) it's not very popular and didn't get a lot of response. I do know why -- it's a prequel in an established AU, it does something completely different than the other story in the series, it focuses on different characters, it's set during an awkward period in the canon; there's too much Loki for Cap or Widow fans and too much Cap and Widow for Loki fans. But it still makes me sad, and it has made me really hesitate on going back to the Yonderverse.
6. Have you written any fanfictions featuring OCs? If so, elaborate!
Yeah, most of them. Marvel's actually an outlier for me because I write very few OCs here, though Home has a bunch -- all the matryoshki but Lorraine and Dottie (who is showing up in 10), Kim Pantcheff and Hana Korematsu from the SSR cryptanalysts; technically the members of the Winter Guard are comics canon characters but that's just me tacking on canon names to OCs. Horizon's got a handful of Asgardian OCs -- Ullr, Forseti, Rota, Signy -- and of course the various Widows and Hulk-Widows are OCs.
Back in Star Wars, Backbone has some very major OC characters -- Alecto, Doriah, and the rest of the extended Syndulla clan being the main culprits, along with every other Twi'lek other than Cham and Hera. (Backbone was written before SW introduced Hera's mother in canon.) Roberto Beneke, Hera's ISB handler, is an OC; the bulk of the Inquisitors are OCs. (Backbone was also written before SW introduced the numbering system for the Inquisition.) Gambit also has a number of OCs, mostly in the Naboo military.
Back in Narnia the bulk of my characters were OCs. Writing in Marvel and Star Wars, there are a lot of background canon characters, both from the mainline canon (films, TV) and from comics and EU, and very often I can just pull someone from there. I only use OCs if there's no way around it. The trick, of course, is to write them without making them seem like OCs and like I am pulling them out of an obscure piece of canon. I've gotten a lot of comments in my day from people saying that they don't usually read fic that features OCs in main roles, so I am cautious about using them heavily; Backbone's a major outlier. (And back in the day I did not think that Star Wars would ever give Hera's mother a canon name.)
12. Do you respond to comments, why or why not?
Except on very rare occasions (usually for clarification), I only respond to direct questions in comments and even then I only do it about half the time.
About fifteen years ago, back in the LJ days, I lost my temper at someone who'd left a comment mixing my fic up with someone else's, and after that I instituted a strict 24-hour cooling off period between posting and replying to comments. Eventually, that changed to a week, and then to only replying to the comments on the last chapter just before the new chapter was going to be posted. I stuck to that for a really long time, I don't remember when exactly that changed, but I think it had to do with when I started getting a lot of hate on Gambit -- I don't respond to negative comments, period, but I felt weird about replying to every comment on a chapter but the negative ones, so often I wouldn't reply to any comments on that chapter. I used to also reply to comments on the first couple chapters of a story, and then just peter off answering comments on the rest of it -- I think I did this for Morning -- but it eventually has just turned into not responding to comments at all. I also don't like answering comments because (1) it messes up the comment numbers on a story and I'd rather that be an accurate reflection of how many comments people other than me have left and (2) I do reread my comments and I don't like rereading my own responses, since they tend to be variations on "thanks for reading, I'm glad you're enjoying the story!" If you want to come talk to me about my fic, do it off AO3; I'm happy to talk about it on Tumblr or Twitter, in person if you know me IRL, but I don't want to do it in my AO3 comment section.
I do respond to non-AO3 comments, i.e. if I'm posting concept writing on Tumblr, I'll respond to those comments. But I don't get that many of them.