Should I replace ALL the fuses in plugs?
Originally, in the UK after BS1363 was introduced, there were 1, 2, 3, 5, 7, 10, and 13A fuses but nowadays mostly 3,5 and 13 are used/available.

The plug fuse is to protect the wire between plug and appliance, it is not primarily intended to protect the appliance (which can have it's own fuse or other protections).

So the choice of fuse principally depends on the diameter of the wires between plug and appliance.

However there is nothing wrong with choosing a lower fuse capacity that will also protect the appliance to some degree.