There is no real consensus as to what constitutes a 'Tai Chi Master'.
Peter Southwood suggested the following guidelines:

•  30-40 years martial arts experience
•  25 years tai chi chuan experience
•  20 years teaching experience
•  30,000 hours of tai chi practice
•  Stage 5 skill with all forms
•  Capable of teaching other Instructors

Some tai chi principles can be applied in baguazhang but the latter involves more movement, stepping and walking. In bagua you primarily have to remember to move or step when attacked but in tai chi you only step when necessary. Sometimes it's hard to switch between the two. Sifu often shows examples of equivalent tai chi postures and this really helps to differentiate the two approaches.
 
 (Rachel Waller)

4 ounces of pressure is easy to say but quite difficult to employ in actual practice because it means stopping every time you encounter resistance.

You must be like sand or water; offering no resistance in your own body and not working against resistance in others.
How is sand or water powerful? Momentum and weight.

What are the 16 treasures?

No, we are not simply going to give you the answer. Finding out for yourself will be vastly more rewarding.

Any tai chi instructor is capable of telling you.
They are the 16 key facets that underpin everything else you do.
16 things that make tai chi work.

All of out students are taught the 16 treasures.
But only the thoughtful, sensitive students sees them.
Without an understanding of their worth, the student may just walk straight past. Then, what has been learned?

Tai chi form begins as a robotic sequence of movements and gradually transcends its original form. Movements become increasingly subtle and internally convoluted, and their power increases.
Instead of being limited by form, the practitioner merges with it to become formless.

This journey does not happen by itself.
Beginners spend ages locked in patterns of tension and external movement, never realising that the form can and should progress.

How does form move from basic to advanced? Neigong.