^ Some people believe that some electronics sound better when 'warmed up'. Maybe true for old school tube amps without preheaters but not so much for solid state.

 

I agree, over coolong is a myth, and even with 50 fans you aren't going to 'overcool'.

I would add up to 30 amps on one relay. If you have 60 amps of draw I would recomend two relays etc.

As for fusing fuse a line to each component with the value recomended by the manufacturer.