Hi, welcome to the forum!
Afraid I don't know anything about rental vehicles, but the Public Transport is great, at least in the larger places!
You've probably found it already, but here's a link to the bus timetable & map -
https://www.iombusandrail.im/timetables-...-and-maps/

Sounds like an epic journey you're making!
Where are you coming from & how long is it going to take you?