Your theory does seems to be connected on some parts but since it’s a romantic comedy as well as a healing drama as per them, I don’t think they’ll give an emotional trauma to their viewers.
We know that SeokRyu would have faced some serious things to take a break for 1 year in the past, and it will somehow impact her present when others will get to know but they’ll eventually be together!
And Atelier In is already famous since we can see in Ep 6 that SeungHyo was being praised by his previous colleagues at the dinner and also when he was showing off his watch to the fraudster he did told him that he received an award recently which clearly shows that everything is happening in the present. So the theory about Ep 1 opening, doesn’t seem to be connected.
I think why she didn’t give proper reason for leaving the job is because she didn’t wanted her family to get more tensed since she is the elder child and her family had high expectations. We could see in Ep 4, when she told Choi Seung about being an outcast in the workplace and somehow blamed her and that could be the reason why she didn’t wanted to showcase herself as weak in front of her close ones.
Although, I am not sure why we saw that choi seung wanted to build shelter of memories but that could be related to something else. But I do hope, since it’s a healing rom-com, we will have HAPPY ENDING !!!