I start every one of these letters the same way, but it's always worth saying: you're awesome and I don't want you to stress out about perfectly matching my requests. If you really love it, I'm sure I will, too.
But I do have details and feels for these fandoms and that might help you out!
1. Dark Shadows (1966) - Any
DS is my oldest fandom, or it would have been had I known what fandom and the internet were when I was eight, and I love almost everything. I realize, however, that that is distinctly unhelpful, so: Barnabas, Julia, and Willie are my three favorite characters, I'd rather not receive a straight-up romance fic, I'd prefer present time (pre-1795, Dream Curse, Leviathans...), 1970 PT, or 1897, and I'm not a fan of the 2012 movie at all (just in case).
2. Baccano! - Luck Gandor, Claire Stanfield, Firo Prochainezo
First off: I'm only really familiar with the anime, not the light novels. Luck is my favorite character, so what I really want is something about him (I love character studies). Definitely don't feel like you have to force this, but my head canon for Luck is that he's gay, so if that works for you I'd be pretty psyched. But as long as the fic isn't Luck/Eve, I won't be disappointed. Backstory fic - gen, slash, or friendship/family - would also be amazing.
3. Strike Back - Any
Another fairly open request. What I'd like most is friendship fic for Scott and Stonebridge, but my character study love is universal and there's no one I don't like. I don't want a romance fic, because that's not how I watch this show, but any gen scenario (action or more introspective) would be great. Feel free to pull in other characters, even if they're not on the list, and I don't have any preferences re: chronological setting.
4. Tinker Tailor Soldier Spy (2011) - Peter Guillam, Peter's boyfriend
And now my super specific request. If you're taking this on, please feel free to include other characters and set it at any point before, during, or after the film, as long as it's Peter-centric and involves his relationship with his boyfriend. I do like fix-it fics, but you don't have to take that angle. Also, I am a fan of le Carre, so you're welcome to throw in details from the novel if you'd like.
And that's all I've got, tbh. I don't want to overwhelm you with details, but I hope this helps a little bit with the plotting process. Thank you so much and happy writing!