I'll keep it short and sweet for the moment, those who can help will be FedExed a free puppy!
1) I'm building a footswitch for my 6505 that will only switch the lead channel. The footswitch works by taking a voltage from the ring of a TRS connector. When the switch closes it connects the ring to the sleeve, which is the relative earth, which lights the footswitch LED, which changes the channel. The question is simple...do I need to earth the pedal chassis?
2) The biggy. I'm building a 6-way breakout box for my pedalboard. The idea is to have a dedicated guitar input, pedal send, pedal return, and then a global output. The idea is to essentially plug in two cables and be good to go... A metal enclosure would make more sense than a plastic one from a shielding point of view, but again...earthing? Particularly since I'll be dealing with guitar signal, pedal signal AND 'to-amp' signal, the likelihood of ground/earth potential loops seems massive. Any ideas?
So you are kinda wanting a pedal looper/footswitch combo?
the metal enclosure will ground the sleeve of the jack to the chassis so you don't need to worry about that.
Same for any other jacks that you have in it so if the footswitch is normally isolated you will want to use a plastic jack or some isolation washers to stop it shorting.
As for the led usually the negative goes to ground but you can set up a spdt toggle with the switching jack so if the led is on in the wrong instance you can just flip the switch and it will reverse the polarity.