obocaman, to sign it it is just using sign apk, I don't know about using it in mac os x since I use Windows 7, maybe you can try with another version of java? Java is quite problematic, and I don't know which version you need in mac os x.
About the bootloader bad arguments, this happens if you don't have the factory.aml file or if this file is looking for a file with a specific name. (usually update.zip, unless you edit it).
Anyway if you want to create a custom rom, I don't recommend make changes and just resign it, because if you don't change your updater-script, probably installation will fail. To create a custom the best thing to do in my opinion is taking the 800 mhz firm base (which is clean) and make the changes from there.