I read your second story (this) first and didn't see the 'challenge' in the comments until I got to the first one. Impressed you went for it!
Also had meant to say here that the flashbacks are nicely woven into the story and really add to it.
As for: "I feel that in switching between past and present tense, I'm kind of pushing the limits of my English skills."........such modesty :) - I think your use of tense works very nicely with the flashbacks. Pretty sophisticated IMHO!
Ah wow, really appreciate the feedback! Thank you for taking the time to reflect on the questions I put out :). I guess not being a native speaker means that sometimes I look at my sentences, and I first try it this way and then the other, and then I'm not sure which way is correct, lol.
But it's great to have a platform like this, and great having people like you out here who provide valuable feedback! Glad the flashbacks worked out!