Copper tubing

Hey all, I am having difficulty finding info on this specific topic, so I am hoping there's some expertise here that can help me.

I am currently deciding on what material to use for my tubing. I know I want metal tubes (something something heat transfer) mostly for aesthetics and the gleam of the metal. I've been leaning towards copper tubing due to the high availability at home depot, ease of manipulation with the proper tools, and its general properties (compatible with other copper in the loop, etc). The issue with this is that copper tubing OD changes by its grade, so I would have to guess and check a little at the store for a pipe that would make a good seal with my fittings. Soft copper does (I think?) have an accurately reported OD. But the clean, straight lines from the mental tubing are pretty important to me, so I haven't really looked into it.

What I see on the brass side is that, while further along the galvanic series, it is still mostly copper. Internet says it has better resistance to corrosion, which I assume is why it seems more popular than copper. My issue is that to use this stuff, I would essentially be bottlenecked into paying a watercooling company $25 per pipe length, whereas I could get all the material I need for a fraction of that bending my own copper pipes and polishing them.

Is the reduced corrosion found in brass very important? I honestly have a hard time imagining that a few years in a water loop would corrode a copper tube in any meaningful way, but I also have to assume there's a good reason the brass tubes seem so much more availible. Do people prefer the brass? Or am I just not looking in the right places? Advice appreciated!

Is there a way to tell if copper is hard/soft after it’s already been installed?