I am not by any means an SMW expert but lately I've developed a keen interest on the SMW romhack scene.

If what you want to do is extract a level and/or play around with level creation the golden standard tool is Lunar Magic [0].

There are some forums with information about rom hacking, level creation, music creation and so on for SMW, like SMWCentral [1].

[0] https://fusoya.eludevisibility.org/lm/index.html

[1] https://www.smwcentral.net/