Cant see any neccessity for Kun to start. Kelechi's done fine and will soon be back on the bench for Kun as the bigger games begin. Yes, I'd start Aleix Garcia. Sends out a solid message to the squad, tests him a little more and I think he'll look even better next to KDB and Gundogan than he did next to Fernando and Angelino. Plus motivates the other players in that position to not rest on their laurels as they can see a young lad stepping up to challenge them for the spot.
I think this season Pep will surprise a lot of people by randomly benching a player here or there for a younger player like Kelechi or Aleix Garcia, just to keep everyone hungry. This is a terrible Swansea team and we'd have a ton of options coming off the bench worst case scenario. Pep isnt Pellers, if it isnt working he'd change it fast enough to fix the problem and get the result.