Do everything you can to get a Fastpass for Frozen - which includes trying on the day it's made available to re-trying periodically until your trip and most certainly several times in the last few days before your trip.
It's the hardest one to get. After that, in terms of wait time, Test Track is now the next longest line - but Soarin's queue is so much more boring to stand in, so I'd Fastpass it next if you cant get Frozen. Can't get Frozen? Get to the park at opening and go right at rope drop. Use the Fastpass for Soarin, and then do standby at Test Track relatively early in the morning. If you get the Frozen fastpass hit Soarin right at park open and then do standby or single rider for Test Track.
Almost nothing else in the park is going to have a particularly long or insane wait time. Most you can time to be 15mins or less just by avoiding them when they are 30-40minutes - particularly Spaceship Earth and Seas with Nemo. Just go later in the day or if you catch them between the other major rides. Touring Epcot "effectively" does require some backtracking. The park is always open 9am to 9pm (or later during the holidays) so you can just go from A to B and whatever is adjacent with minimal park crossing and still do everything, or at least enough that you feel like you got a good sampling.
In terms of "what can i skip?" The Circle of Life film in the Land pavilion is just a time filler - go watch a recording of it on YouTube if you really feel you're missing out. I think Turtle Talk with Crush is cute but I'd not give it any major chunk of time - if a show is starting right away when you're there then you might as well, but otherwise, meh. The entire Imagination pavilion.. just.. meh. I used to love the Universe of Energy but it's old and clunky and outdated so go for it if you feel like you're making good time and also want to get out of the heat for 45mins (yes, it's that long.) If Innoventions is still open, don't set foot inside of it. Just don't bother.
Pretty much everything else is worth doing and making the time for, with the caveat that you said you were interested in the cultural aspects. Most "ride junkies" wont like seeing all of the World Showcase films but if that's what you're in the mood for they're perfectly entertaining. Just remember that American Adventure is not a film and so if you see one and are like "meh" keep in mind that American Adventure is not that
Also, hit the museums. There's one you have to walk through in Mexico to get to the interior of the pyramid and the ride, but the others are less obvious. The Stave Church in Norway is a thing you can go into (many people don't realize this) - as is the Gallery of Arts and Sciences in Morocco. Bijutsu-kan Gallery in Japan is cute (literally, the current exhibit is "kawaii" culture.) House of the Whispering Willows is directly adjacent the film in China. Explore it instead of just sitting on the benches in the holding area.
Many people just stay on the promenade in World Showcase and then feel they've seen the countries. Many have no idea there's waterfalls in Canada or that there's a whole hidden shopping district in Morocco. Go -into- the countries.
