Hi Bisapaca
from Spilt to Stari Grad, you have 6 or 7 daily departures, so that should not be problem to get there.
From Stari Grad to Korcula you have ferry on mondays 8.40 AM.
Korcula - Orebic, ferry leaves every half hour or so, just go down to terminal and line up
for the trip Hvar - Korcula you can buy ticket online, and pick it up when you get to Stari Grad
For the two other connection you buy ticket when you are there.
regards
Morten