The ability to lift heavy weights, run, swim or workout in the gym may well improve your overall fitness level.
But this kind of fitness only helps to a certain degree in internal kung fu training.

A student must learn how to use their body in a very different way.
The body needs to become agile, flexible, adaptive, sensitive and strong.
Engorged biceps are not going to help.

Remember that your aim is not to make an impression.
You can accomplish this by looking at various ways to lessen your presence:

1. Attire
2. Deception
3. Keep to yourself
4. Possessions
5. Slow
6. Soft
7. Sound
8. Talk

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.