The best beginning place for development is to read se-developers.net. As it's only available on archive.org, I have created summaries of the accessible threads.

My se-developers backup collection: sedevs_all.zip

se-nse.net v5 forums
se-nse.net v6 forums
As it's necessary with se-nse on archive.org to play with timestamps for archive snapshots, I have created summaries of the threads.

My se-nse backup collection: my_se-nse_collection.zip

There was also an official se-nse backup: se-nse.rar. I have already merged it with my own collection.