I think I'll start with that, actually. Still, having a num digit limit for the score is probably good anyway.
So, a cap of seven digits and 1 sprite for "1p" or whatever -> 8 sprites, 18 tiles of vram.
Gold coin counter, 1 gold icon and 3 digits -> 4 more sprites, ~10 tiles.
And one sprites for the elemental attacks. Was thinking 3 sprites, 12 tiles.
Sum: 15 sprites, 40 tiles. Well, the HUD is a huge part of the game so I'd say it's worth it. Or maybe I calculated this wrong?
As said, it's a start and I can just change it if the need should arise. Even Hagane uses a black window, so I can always go that route if all else fails.