There are several things that get called reverse protection diodes. One is the diode that protects the 7805 from an un-powered supply line. That one very much does do it's job. Leave it out and the regulator will smoke when the +12 is off and the USB is supplying power. The reverse diodes that you see on the FET's are there to keep a switched inductive load from over-voltaging the FETS. For that they do an excellent job, they are not there to protect against a supply reversal.
Running 12V fans on 5V is not a good idea long term. They gum up and stop working. Finding 5V fans is not as easy as finding 12V fans. Running the current down to 5V simply increases the power you dump into the 7805. You will need a lot more heat sink on the 7805 if you try to run 5V fans off of it. It's not just a matter of whether the 7805 is rated for 24V, it's the power / temperature rating.
If you go with a 16A fuse, be sure to also come up with a power connector that's rated for 16A. A fuse (any fuse) is rated to carry it's labeled current. It will cut out at a current well above that level in some amount of time (might be 30 minutes, could be longer).
I just noticed that your schematic has the fuses in the ground return on the FET's. If they are there and you have a load short to ground, there is no protection at all. Your board smokes. It's just as easy / cheap to put them in the supply side and get protection for both the FET and the load short.
Running 12V fans on 5V is not a good idea long term. They gum up and stop working. Finding 5V fans is not as easy as finding 12V fans. Running the current down to 5V simply increases the power you dump into the 7805. You will need a lot more heat sink on the 7805 if you try to run 5V fans off of it. It's not just a matter of whether the 7805 is rated for 24V, it's the power / temperature rating.
If you go with a 16A fuse, be sure to also come up with a power connector that's rated for 16A. A fuse (any fuse) is rated to carry it's labeled current. It will cut out at a current well above that level in some amount of time (might be 30 minutes, could be longer).
I just noticed that your schematic has the fuses in the ground return on the FET's. If they are there and you have a load short to ground, there is no protection at all. Your board smokes. It's just as easy / cheap to put them in the supply side and get protection for both the FET and the load short.