Driving in Malaysia is fine as long as you're alert. No worse than, say, Boston or Phladelphia. Driven 2x between Penang-KL-Melaka (and Johore Bahru) r/t and it's fine.

Rent a Proton Saga and you won't have any problem with speeding tickets: They don't go fast enough. I've rented through Sixt (local franchisor) and Avis. Both are fine.

I've come across a local outfit called Mayflower (no direct online reservations except indirectly through some sites such as Scoot) that rents some Nissan (Sentra equivalent?) as their base model. Anyone ever used them?

As for GPS, if you have a Garmin, this site has free maps (and speed cam proximity alerts). I only use the GPS in north-up map mode so not sure how it is for fly-behind navigation.