If it's any help, you can take a look at my disassemblies of Zelda 1. There is plenty of comments in there.http://www.bwass.org/romhack/zelda1/
The disassemblies are named "zelda1bank0.txt", up to "zelda1bank7.txt". There's also "zelda1rammap.txt" for descriptions of RAM addresses.
Concerning the cracks in the walls, there is a specific set of tile mappings for the bombable walls (both for Overworld and Dungeons), but they simply are set to the same values as normal walls. The entries do exist, so assuming you have the space necessary to store the new graphics, it will be easy to assign the new tiles. Check my docs for Bank 5 at $15FEE.
About the graphics. I'm not particularly fond of the Link's Awakening style, but I watched the gameplay, and the graphics are indeed very good. They look a lot less flat than the original, and many sprites have a better use of the [limited] colors available. Kudos to that.
One thing I'd like to see is to have a proper "X" sign beside the rupee, bombs and keys counters in the HUD. The original game uses the letter "X" and it looks weird. I think the graphics would allow for an extra tile, but some relocation of graphics data would be necessary.
If I have time, I could see if there's something we can do about the Magic Wand and Wizzrobes. Also, the problem with the 999 rupees. I would advise to consider letting this feature go if it becomes too troublesome. I think having a maximum 255 rupees is not that bad.