Treasure Rush!! - Tilesets

Here are tilesets for a NES-styled game I'm working on called Treasure Rush. It's a platformer in which you explore levels to find hidden treasures.
It's currently a work in progress, I'll post mock-ups to show the tilesets in action.

Hey those are pretty cool. I'd like to see a mockup.

Not bad! Definitely want to see a mockup or two.

...though if I can nitpick one little detail, checkerboard dithering can create horrible patterns on composite. Be sure to check with an NTSC filter (or the real thing!) at some point, if you intend this to run on hardware.

Nice. Wish I could draw at all. PS. I converted the BMP to a PNG in case someone's afraid of the file size.

I've posted a few mockups which are mostly screens.

While I don't intend to make it an actual NES game, I'm not exactly sure how many tiles you can store in a ROM, assuming it's 256 KB.
As for the game, it consists of 50 levels including boss fights, but unless the levels take place on a single screen, that seems too much for an NES, so I was wondering if there was a limit on how many screens a game might have as well.

The number of tiles that you can store depends on the "mapper", or the exact configuration of memory and other hardware on the cartridge board. Your guess of 256 KiB (a total of 16384 8x8-pixel tiles) is a good first approximation. But there are other limits seen in common mappers, such as switching 64-tile (1 KiB) pages at a time (if your mapper uses CHR ROM).

There's not much of a limit to screen count, particularly if you can figure out a compact storage format for the levels. The practical limit in games of the era was 256 KiB of program, including code and level maps, though a few later games were bigger. But all the map data in Super Mario Bros. is on the order of 8 KiB. Show a typical level map, as might be seen at vgmaps.com, and I might be able to reason out how much memory it'd use.

While there's definitely a limit on how many tiles can be used at a time and in total, there's no hard limit on how many screens a game can have. If they were randomly generated, you could even have an infinite number of screens! It all comes down as how they're stored in ROM. Take a look at this very interesting video by Morphcat Games explaining how they were able to cram a whole bunch of screens in such a little ROM. It may not be immediately noticeable to players, but most games have a set of constraints around how their levels are built, which are side effects of the techniques used to compress them.