GPS and satphones are definitely among the devices that will be confiscated and kept for your departure.
Renting is like anywhere else - I haven't looked, but it seems Europcar is everywhere. That means be careful check the car out very carefully for faults and missing items, photograph it all, etc. etc. and given you are required to purchase insurance when renting a car as well.
http://www.carrentalcuba.com/havana_...ire.asp
http://www.rentacarcuba.com/service_...idioma-eng.htm
www.havanautos.com
www.transtur.cu
etc. Google
renta autos la habana and you'll get a lot of listings.
Also beware - some Cubans are happy to rent you their cars. This is not legal, and it's definitely not smart, in terms of mehcnaical reliability and if anything should go wrong (stopped by police, accident, breakdown, etc.)