Check for error traces in the bench start output or your browser console.
That depends on the complexity of the task you wish to accomplish. Sometimes only a few changes in the doctype form can get your work done. Other times you may have to write JS and/or Python code. If you can list some cases, I can write you a better reply.
I’m not sure what you mean but what kind of changes. Adding or removing fields /buttons ? Or is it something changing CSS ?
I’ve included some more tips on this post of mine. Read it : Suggestions for new users for making good posts on forums