Horton pulled in the 3rd after allowing a swinging bunt single to 3B; getting another swinging K (on a fastball); and a jam-shot bloop single. He was at 47 pitches.
You may be right. Milb.com lists Michael Arias as the starter today, although it's fair to note that they get it wrong plenty of times throughout the year.
Paciolla was plunked in the wrist in his very first PA in EXST and exited the game, per AZPhil. Hopefully it's just a bruise.
https://www.thecubreporter.com/cubs-edge-giants-extended-spring-training-opener-papago-park
AZPhil's list of stretched out pitchers for SB is Birdsell/Hodge/Little/Gallardo/Connor Noland/Adam Laskey/Adam Thoreson. Kohl Franklin is listed as on the roster but isn't stretched out.