OpPa

Oppa also means older brother in korea, dude. ಠ_ಠ

Is does but like with niichan/oniichan depending on how a girl wants to use it, it can be either she's close to him (classmate's older bro so works) or trying to be cute to him in a flirty way (he did save her life and hes super cool so ya never know).

While blushing...duhhhhh

Yeah, in the light novel they didn't mention if she blushed or what. So I assumed it's not that kind of "oppa" ╮(￣▽￣)╭

Havent read the LN so wonder if they're gonna take some leeway with small things like that.

Have they added or taken out anything somewhat major?

Nah, as far as I can see, they're on the same track as the novel. Which is really exciting because it will get even more intense as the story progresses.

If you want to read it, this website have a pretty decent translation. Start at ch. 65, it's the same as ch. 55 in manga. :)
https://www.readlightnovel.org/solo-leveling

Thanks dude/etter *^*)b