1) Casas will be fine. His issue is mostly an approach issue. Hitters with his blend of patience and power almost always take time to adjust to the quality of major league stuff, and what pitches they can take and what pitches they can drive at the ML level. His passivity can only be remedied with PA's. He's in the top 4% of the league in BB%, and he's 68th in MLB in average exit velocity , 78th in barrels, and 50th in barrels per plate appearance. Dude has patience, hits the ball hard consistently, and with good angle. He will rake.
2) Duran doesn't need to be a great hitter to be an important contributor to the team, but he has a good batted ball profile, and has shown elite defense and sprint speed.
3) This lineup should lean a little more RH considering the stadium they play at.
4) I don't think Paxton is the piece in this rotation that needs replacing.