What will happen if a flow starts but does not finish running and the next schedule run of the same flow runs again ? is there a way to get some kind of alert if this happens ?

Hey @YD, so the next one will run. If you are in the standard tier of Cloud, you can use Flow Run Concurrency Limits where the next scheduled flow will wait for the previous one to finish is there is a limit.

Does STANDARD has a monthly fix fee, or just the < $0.0050 per successful task run ?

You are only billed per successful task run more than 1 second