Looks fun so far, and great pics!
I don’t know if it’d be worth the expense to you, but you might consider some end mills for boring a hole in copper or weird objects like that sink. Would necessitate good work holding in a vise and assuming the chuck doesn’t have appreciable runout, everything is pretty well squared up, etc. I picked up this chinese carbide set and I’ll be darned they are excellent for everything I’ve been able to use them for while abusing my drill press. Quite sharp and well ground, true end cutting/plunge face, and have breezed through lots of different hardwoods, a few plastics and a little linen phenolic…some very light (and careful) use on 6061 as well, still sharp. This made it easy to “plane” a little chunk of sycamore I had for a project. But for boring that copper I think it would do well if you can keep things solidly held.
I’ll link to these because that’s what I bought but there are a few sellers of the same mills….and lots of other mills that are not that great, which includes just about all of the chinese HSS versions, most of which are not true end cutting mills and so would be unsuitable for plunging/drilling like this. You can get these on aliexpress a bit cheaper (or used to be able to) but then you risk not getting what you thought the photos showed…so. They may have some individual sizes on amazon as well (definitely do on ali).
https://www.amazon.com/gp/product/B07TWTZRQZ/
The more machinist-worthy cheaper import mills are considerably more expensive usually, individually. Anyway, just a thought.