You seem to have gotten some interesting and varied advice. From your posts, you also seem to have a fairly deep grasp of many principles. Given that, I am not sure what I could add.
There were few things that did strike me from your posts. Perhaps, my comments might be helpful.
<font face="Verdana, Arial" size="2">for a year I find that I have no improvement in internal enery. </font>
I think a focus on internal energy is very good and is one of the essential questions for everyone.
<font face="Verdana, Arial" size="2">I can feel my chi, but it does not get stronger. What can I do to improve?</font>
I find talk of strengthening chi/qi always to be a little strange, not only for the reasons other posters have given for not focusing on qi, but because I do not think "strengthening qi" is a direct focus of Yang Style. I think the initial focus should be on learning to let the qi flow in an unobstructed way. Some people use terms like "strengthening" loosely to mean unblocking the flow, but I think the distinction is very important.
If you eat an apple, you have more qi. If you lift weights, you will generate more qi. Are these activities, however, very relevant for improving your Taijiquan? For me, the difference between increasing my qi and letting it flow more freely is fundamental. The former happens naturally by learning to do the latter and doing it repeatedly over time.
<font face="Verdana, Arial" size="2">I practice both Chen and Yang style. I currently and personally more prefer Yang because it is simple big and soft.</font>
You state that you prefer Yang Style, but when you list the main principles you try to adhere to, I find little of Yang Chengfu there. Do you do some other type of Yang Style? Aren't the principles you list more from Chen Style than Yang Style?
It is not that I find the principles incorrect, but rather I do not see many of the principles that are stressed in the Association. (E.g., the Ten Essentials) If you are not satisfied with your progress, could it be that you are not prioritizing the right principles?
As I review your list, everything seems like some version of mainstream Taijiquan; however, the only two statements I would accept without qualification for the specific flavor of Yang Style Taijiquan as practiced by Yang Jun and Yang Zhenduo are: "I will first calm down my mind" and "I feel the slow movement and low big stance is more difficult." All the other ones seem to take a slightly different approach to the theory than what I understand.
<font face="Verdana, Arial" size="2">Everyday, I spend most of my taichi time on single movement practice which I think is more useful to understand the essense. But I will do the whole forms two or three times a week.</font>
Why do you think single movement practices if more useful to understand the essence? There are certainly practitioners who de-emphasize the form, but I do not think of this is a mainstream view. If you do not have close access to a good teacher and practice the form only two or three times a week, I think it will be hard to make good progress.
In my view, the best use of Yang Chengfu's form is to learn and internalize the principles of Tai Chi movement and to deepen understanding of the Ten Essentials. On the other hand, single movement practice with a partner is good for practicing applications and learning variations, especially after you have a good foundation in Push Hands. Single movement practice by yourself is a good way of understanding the requirements of certain postures and to practice them extensively.
Are you familiar with the Ten Essentials? I judge my progress by whether I increase my level of insight into them. They seem simple, but I believe each of them has quite amount of depth and subtle implications for the movement theory.
I hope this is helpful.