Hi, hiring a driver for the entire trip has been done before, but it can be expensive. Generally the best approach is to use different drivers as you need them.
If you are staying mostly in the city then you can find drivers everywhere. Along the main roads there are dozens of taxis that pass ever minute and a short trip across the city would only cost about 10cuc.
Trips outside the city are more expensive but for about 100 to 150 cuc you can get to most places on the western side of the island. Going far east is a bit more expensive.
Hiring a personal driver who will be with you all day would likely cost about 100cuc for days that you stay within the city and about 150 to 200cuc for days you leave the city. If you are going to really do a lot of driving, then it is an OK value. But let’s say you decided to go from Havana on a 24 hour drive across the country… The driver would probably want extra money anyway.
I get asked this question often. 99% of the time it is far better to just use different taxis as you need then. The only time that I remember a person using the full time driver for multiple days was because the guy had large camera equipment and was going to be taking photos all over Cuba over the course of a week. So he wanted to have one driver with him always to get him around and keep the cameras in the taxi.
If you have more questions, just ask.
Mario