So there is obviously no end of information about Swiss mercenaries on the battlefield, they were a force to be reckoned with after all, but I can find a lot less readily available information about them off the battlefield.
I have a whole bunch I'd like to know, and have found various bits of information about a lot of it that I won't mention here so as to not mix up replies, but in general the points I'm most curious about is as follows:
Thanks for any insight you can give.
This is a bit of an older post but since you haven't gotten a good answer yet, I'll try to give you the information I have. I study history in Bern, Switzerland and I have done some research on Swiss Mercenaries or "Reisläufer" as they are called.
Where did the individuals come from, both those in command and the foot-soldiers?
The leaders of mercenary companies were usually low nobility that wanted to make some money or "professional" mercenaries that worked their way up to being "Söldnerführer", mercenary leaders. The Reisläufer themselves were mostly workers and farmers that had been recruited by the Söldnerführer to join their company.
How were supplies, equipment etc organised?
Equipment and supplies were generally supplied by the company leaders and funded with contract money although sometimes the Reisläufer provided their own weapons.
Who decided where they went to fight and on what level was this done; did a whole Canton go off to war, or were there smaller units that could be hired?
The companies were hired by whomever needed them, the company leader decided what "contract" he wanted to pursue. Generally, Reisläufer companies were not coordinated on a cantonal level. However, the Swiss didn't only fight as mercenaries, when they fought against a common enemy, there was coordination between them.
Were they trained to work together just in their 100 man blocks, or was there extensive training of battlefield manoeuvres involving a whole Cantons forces?
There needed to be some training and coordination within companies but I'm unaware of any large scale manoeuvers.
And, possibly straying into battlefield organisation a bit here, were there uniforms, and if so based on what?
The Reisläufer didn't wear uniforms of any kind as far as I know but I haven't researched battlefield organisation a ton.
As a closing remark I would like to say that the Reisläufer were a very heterogenous group and that the way they operated changed significantly within the ~100 years they existed. Generally, cantons didn't organise mercenary companies, those were formed by independent company leaders. I can provide you with some literature on the subject if you would like but most of it is in German.