I'm pretty sure that ICN has international transit without clearing into Korea but hopefully someone else will confirm. you might check the ICN website to be sure, regardless.

Are the tickets sold as one ticket? You said same airline, but didn't specify if same ticket. If same ticket, and your flight onward from ICN isn't the last of the day, I'd say you should be fine.

I echo the comment above that Osaka is a gentler introduction to Japan than Tokyo, though I wouldn't make it a huge factor.