Where do I check how much storage a single album is eating?

Two places. The Album Edit page shows an "Album Size" figure for that specific album, and the File Manager header shows the overall hot storage picture — something like "132.6 GB used of 2000 GB" with a percentage bar. If you're trying to figure out which of your old albums is hogging the most space, the edit pages for each album will tell you quickly. It's a question worth asking before you hit the ceiling mid-season.