The patchwork elephant of websites means that there isn’t one answer for everything.
With great freedom comes some very odd responsibilities when it comes to reselling products.
Stealing GPL isn’t impossible, it happens more often than I’d like, and it could be easily avoided with a simple attribution of effort.
A non-technical how to get your plugin in the WordPress repository.
While the GPL allows you to fork plugins, you should think long and hard if there’s a reason you need to do this.