I've been wearing Superfeet insoles for a little over 3years. When I was training for a JMT thru-hike I started to have some foot problems and the salesperson at REI suggested I try the green ones. They made my feet feel instantly better. I have continued to wear them in all of my shoes since. I do use the blue ones for non-performance shoes.
To answer your questions:
1)If you have not experienced any problems, I wouldn't change anything.
2)I have always purchased the size appropriate for my shoe size. They have always fit without trimming no matter what type of shoes I have put them in. I have medium width feet and have experienced no width problems.
3)The Superfeet will "break in" in as much as they will mold to your feet somewhat but not to a great extent. I don't feel any break-in period is necessary. My biggest question was always how long do they last? I used to replace them automatically every6-9 months but now I wear them until they are visibly worn out.
4)While I now wear Superfeet in all my shoes, I didn't used to and I don't think it was any problem switching back and forth. I have been bothered by plantar faciitis and feel that they provide good arch support.
5)For me, the main advantage is the arch support and help in reducing a mild case of pronation. I also found them particular helpful in reducing the impact of rocks on the bottoms of my feet on long trail days (20+ miles). I am certainly no expert on feet but would refer you to "Fixing Your Feet" 4th edition by Wilderness Press for more information.
6)I have not had custom orthotics. If you are referring to the custom fit Superfeet, I have no experience with those also. I did just buy a new pair of Spenco insoles that are specifically designed for day hiking. They also make a pair for heavier, traditional backpacking loads. I do not have enough experience with these yet to really know how they will work, although they are comfortable and they do have a few nice features that the Superfeet do not. They also cost a little less.
Prior to 2005, I had never worn insoles in any hiking shoes. BTW I wear running shoes not boots for hiking. However, I am now sold on Superfeet. I have friends who have also had minor foot problems and, at my suggestion, they purchased Superfeet and they have continued to wear them also.