As long as you need that many.
That is the advantage of using the more "complex" fuse blocks...instead of needing two fuse blocks, one for ignition power and one for constant, you can run the more complex fuse blocks and run whatever power source, to whatever fuse, you want. ECM, radio, lights, whatever on constant 12V, while things like electric fans could be run from the ignition switched leads.
In my case, 6 additional fuses were more than enough. But if you are adding a bunch of stuff, two would be easily done as well. But might as well run two "ganged" panels (single power source) if that is the case. Typically you'll only want either constant 12V, or ignition switched 12V. Two ganged panels would give you both.