I recommend getting the amp re-tubed and re-biased by a pro. I don't think the fuses need to be changed out, never heard of that as a maintenance thing anyway...

Some Marshall cabs are stereo, but only if it has 2 inputs on the back. They also say they are stereo on the back near the inputs if it is stereo.

The golden rule for tube amps.....never turn the amp on without it being connected to the cabinet. Even with the standby switch off....This can and will fry your amp quicker than anything else.