If you get to Fuerteventura and rent a car you will know places that are somewhat more isolated and where you would not arrive with buses. For some sites, it is even convenient to carry a all terrain.
You can hire your rent in the same Airport, upon arrival, but if you do it in advance you will surely get better deals. The tariffs They vary a lot if you hire for a few days, a full week is always more convenient. In general, the value for money offered is excellent.
The requirements They vary between companies. At least you will be asked to be 21 years old and have a one-year driving license, identity card and credit card in your name. If you want a high-end car you must be 25 years old or pay daily surcharges. Another possibility offered by some rental companies is that they allow you to take the car in ferry to Lanzarote.