I just coiled 50' of 3/8th copper for an immersion wort chiller, kinda want to zip tie some of the coils together to give it some sort of structure, but not sure if I need to worry about a reaction between Stainless steel and copper.

Use bare copper wire?

isn't having spacing better technically?

What will actually happen depends on a lot of things but copper and stainless are not that far apart on the galvanic series chart. More practically speaking, I've seen enough copper/brass/bronze joined to stainless (valves on the nipples of stainless steel kettles would be a common example) to think that it isn't much of a problem.

don't worry about it.
They won't start reacting.