Re: Taichi and IP/IS
The problem statement with seeking out internal strength as a subject area to learn is that lots of folks are offering internal strength benefits, which may or may not be measurable or related to what's actually described as internal strength as expressed by martial arts exponents.
The best solution that I can offer is to see what people are doing when they describe internal strength. Then think clinically about where the similarities and differences may be. Then figure out what makes sense for you to partake in from a developmental perspective. The worst thing you could do, in my opinion, is do practice X from Person A, then mix a little process B from Sensei C, then stir them up with martial art 1 from Sifu 2. That's a pretty guaranteed way of not getting anywhere as my experience has been that to make progress, you need to condition your body while you develop your skill/sensitivity (has both mental and physical components). Too many distractions or approaches to the baseline stuff (especially when there are differing views on the entry points to the baseline stuffs) will make it so you stay stuck at figuring out what the baseline stuffs are rather than moving past them to the real work.
I visited a local tai chi class as well. As soon as I put my hands on the instructor, I could feel they had no jin (ability to direct the powers of ground pushing up or gravity pulling you down without overt movements) so therefore anything else they were going to show me with regard to internal strength was going to be a waste of time. I moved on.