Well, I think you are mistaken here. There is an Open Source Community Edition of all versions of Pycharm if you are so inclined to the Open Source. That is quite good enough. Celeron is quite old and slow and it is not fair to expect an IDE to work fast on that old PC. Though you can still disable some advanced features( inspections) and make it reasonably fast.

Again, it totally depends on the project you are working. For a reasonable sized project, you can do away with an editor. But with large codebases, IDE support is a great difference. And this is coming from someone who has been writing all his code on Vim for last 6 years or so. Basically, all you require is a productive environment that doesn't hold you back and enables you to write faster and correct code. For me and a lot of other people, Pycharm is quite that tool.