In short yes, there is an ungodly hard mode to CV3, there is no easy mode in the original title. Enemy damage is calculated on a level by level basis, the projectiles in stage 1 only dish out 1 damage (the smallest amount in the game) The only 'easy' version I have heard of is CV3's JPN release Akumajo Dracula. The damage is not based on level, its on enemy type (projectiles from bone towers will always be 1, instead of taking 2 and 3 in later levels). From what I have heard, parts of JPN's code is still in ROM, it might just be a dead end though.
Non related NES facts:
The console can work with 16 active colors (plus one if your really working your hardest) at its max. This is separated up into 12 sprite colors and 12 BG. Each of these 12 colors is broken up into 4 colored banks, all banks MUST share 1 color (known as the base color) this leaves 3 active colors and 1 transparent one in the case of sprites.
The console can only generate 4 colors in 16x16 blocks (although the newest MXM-0 cart may bring that down to 8x8) sprites that have more than 4 colors use whats called a sprite overlay, where 2 palates lay on top on one another to simulate more than 3 colors, this technique takes up a lot of space, so be sure not to go to crazy with that fact.
The NES can render up to 8 8x8 tile sprites in one scan-line, you can push that limit by sprite flickering, however this can cause slow down.
Im not a programmer, but sites like https://bitbeamcannon.com/nes-graphical-specs/
may be able to help.