I like your idea about spending just one hour on e-mail. I used to check it several times a day. Now I check it twice -- once in the morning and once in the evening. As I check it, I add anything that needs a reply to my task list.
Like you, I am a one-person business and it is very easy to become bogged down with administrative duties. I have tried several task managers including an on-line application but either they were too in-depth or not deep enough.
Recently I found a GEM of an app -- NoteCase pro. It is a cross-platform outliner that works in OSx, Windows, and Linux. The more I use it, the more I like it. In addition to easy task management, it keeps tracks of all my notes both business and personal so that absolutely nothing falls through the cracks. There is a free "NoteCase" version, but it doesn't have quite all the things I need. While NoteCase-Pro is not free, it is quite inexpensive and offers several licenses. If you want to configure things so that you can do them your way, it is certainly worth a look.