Have you followed any of the links to Amazon, EBJ, CDJapan, etc and bought any copies of your favorite manga?
Amazon: Yes for physical copies,
EBJ: never used EBJ because I haven't figured out how to rip from there yet, so I use Bookwalker as my preferred digital choice, especially for their covers,
CDJapan: only if I can't find it on Amazon or if it's cheaper on CDJapan, and sometimes CDs themselves as that's what I originally used them for and still mostly do because the physical CDs I want on Amazon are often sold out or overpriced. And yeah, I still occasionally buy CDs... I'm pretty old school, so what can I say. I mainly to rip them digitally and keep the physical copies looking nice and neat on my shelf.
To check: daily...because I like to keep a personal record of each and all the series I follow on my hard drive along with all available links, genres, descriptions, alternate names...etc
To buy: it used to be monthly, but then IRL priorities shifted so it's now every 5-6 months or so, which coincides with when a new volume is released.
Excluding my favorite series, I typically don't buy series
as they're being released, opting to wait until it's all out so I can buy it all at once. The reason being that I don't want to buy say up to 3 volumes, then find out I want to drop this series because I don't enjoy it anymore. The downside of this practice is that volumes sometimes go out of print before I can get my hands on them, which is why I'm forever grateful for this site and archives existing.
And if you are willing to share, how much have you spent?
For the reasons mentioned above, it's hard to say. Really depends on when they're released. But to estimate, probably anywhere from around 60-120 a year for Japanese volumes. I probably spend more on English volumes every couple of years, since I almost always exclusively wait until a series is complete before buying.
What do you actually do with your copies, if you can't read it?
They go on the "To read" shelf or if it's digital, I keep a rather unorganized mess of memo list of titles and read from Bookwalker's servers when I'm done finishing a current series that I'm reading. That being said, ever since mangadex came around and became so much more user-friendly than Batoto, my rate of adding new unread series to my list far outpaces my list of series I finish reading. I guess that's a good thing since I find lots of new series that I like.
Would a list of upcoming releases for new volumes interest you if we had it on the site?
Absolutely; ideally for both Japanese releases and North American English.