Hertz at EDI I have used a dozen or more times.

Your journey should start at EDI and not anywhere in the city as the city is a nightmare for driving. Getting out to to EDI and the car hire centre (all brands are co-located there) is easy as the tram terminal is beside it.

It is easy to get to and from the EDI terminal when heading off to the highlands.

Do not get an EV under any circumstances as the infrastucture is not yet mature enough throughout the highlands unless you have assured charging at your destinations. Just practical advice as I am not an EV hater. I am a Tesla owner and I live in the highlands!