Your schedule looks fine. I reckon a 05:30 departure from Salema is fine. 90 minutes max to Faro airport at that time of day.
You need to be at the bus station no more than 30 minutes beforehand to buy your ticket.
However, if you are in Lagos over the proceeding days, you could pick up your ticket in advance from Faro to Seville at the bus station in Lagos.
