The only way I know to "loosen" the coils is to braid it. But I don't care about loosening the curls. When my hair is drenched with S-Curl spray, it combs so easily and the coils look so cute that I simply couldn't change that. But I do know that the reason I can go for months w/o using a comb is because the braids or twists keep my kinks somewhat stretched out so that the hair strands don't coil around each other and can be separated w/ fingers.
I do DC in braids and I've never had a problem with not rinsing the product out. I am in braid extensions and usually DC with Aubrey Organics GPB or Emergencée followed by a shampoo then a moisturizing conditioner like Elucence. I do rinse for a loooooong time after DCing and the shampooing after Emergencée helps, I think. I have never done oil rinses. Many years ago, I used to do hot oil treatments but I cannot remember what difference they made. I was relaxed then, if I'm not mistaken.
I never straighten my hair to trim. I don't usually trim it all at once either. I'm a bit strange like that. I usually look at the ends of each braided section as I rebraid one at a time and snip off the ends if they don't look tidy. Sometimes I do this randomly only trimming each section as it needs redoing; other times I'll start from the back and redo the braids one at a time dusting the ends as I go along. I just stretch the hair section so I can be sure all the hairs are about the same length then snip off about 1/4 inch from the end. Because it's curly, I probably snip off a little more than 1/4 but I reckon that I'm better off getting rid of as much of the bad ends as possible than leaving a tiny bit of split that will just continue to tear down the length of the strand. One thing I love about having curly hair is a small difference in length like say half an inch will not be the obvious, so for the sake of having healthy hair, I dust w/o caring about the hair being perfectly even. I reckon when I'm ready for a stylish cut, I can get a pro to even it out. But for now, I'm after health rather than perfection.