I visit 3-4 times per year (my daughter is a CM). I usually stay at the Grand Floridian. I never book ADR's. I always just book dining as I go. Everything is always available. Well, maybe not everything, but nearly everything. Just back from a weekend trip this past weekend, Friday-Monday. Every day, every meal, I checked dining availability and had almost every restaurant available including "hard to get" locations like Cinderella's Royal Table, Space 220, O'hana etc. You will have no trouble getting reservations at the monorail resort restaurants. Do not sweat the ADR's.
Steak - I love Steakhouse 71 at Contemporary. Narcoossee's, Grand Floridian Cafe and Citricos at the GF are great and have good steak.
Ribs - I'd have to look at menus, but I think the only spot with ribs is Whispering Canyon at Wilderness Lodge? I'm not sure.
Buffet - Best dinner buffet hands down is 1900 Park Fare at the GF. It's Grand Floridian culinary food. The Prime Rib, Salmon, mashed potatoes and other sides and desserts are are high quality and awesome. Characters are good. Other buffet option is Chef Mickey's at the Contemporary which I dislike, finding it loud and obnoxious and the food not that great. Ohana is not a buffet but an all-you-can-eat. I don't personally like the dinner food at Ohana, but many do.
So every day whenever I start getting hungry, I check dining availability. Tons of choices. There's a spot on the
MDE app where you can check Walk Up. I often saw Steakhouse 71, GF Cafe and Citrico's available for walk-up.
Side note - don't forget the bars. You can eat from the regular menu at the bars at Steakhouse 71, Narcoosee's and Citricos, no reservation needed. Every trip, I eat dinner at the bar at Narcoossee's. I just stroll in when I get hungry. I hate being locked in to reservation times. The Narcoossee's bar is beautiful, view is great, staff is great.
You mentioned Captain Cooks at the Polynesian. That's a quick-service restaurant. I do like their meatballs, but if doing quick service, I personally prefer Gasparilla Grill at the Grand Floridian. I also like the Tambu Lounge bar snacks upstairs at the Poly (next to O'hana).
Sorry for the long note!