In all the resorts you will find a bus timetable at the main bus stop. You can also find English language, local newspapers, such as the 'Corfiot', which has a section detailing bus timetables.
Yes, the local bus service is very reliable, however, you should be at bus stops at least 10 minutes before departure time, if a bus arrives early it will rarely wait.
You should arrange a price with the taxi driver before you set off. Prices may vary according to resorts and distances.