Coming in late but I've been doing BKF material on and off for a number of years starting with energy gates book and have also purchased a few online programs.
The first thing to understand is that BKF teaches a pretty specific "16 Neigong", and the various movements he teaches (Energy Gates, Heaven and Earth, Gods Playing in the Clouds, Tai Chi, etc) are "containers" that allow you to embody the 16 neigong. He teaches different sets because different sets are better for different things. Energy Gates gets the downward current going, which BKF is big on, Heaven and Earth helps opening and closing, things like that. Ultimately, an advanced practitioner is going to be able to embody them doing any movement, but some are better for learning than others.
So with that in mind, the goal is not necessarily to "mix other practices in' with Energy Gates", but to continue doing Energy Gates (or whatever your practice of choice is) and as it deepens and you awaken more of your energy bodies (BKF has his own 8 energy body breakdown as well) you will embody more and more of that in your practice.
Now here's the kicker - BKF studied with a number of teachers over the years, and they didn't necessarily give him everything that he is putting out. He pieced it together himself over the years and when he met his final teacher, Liu Hung Chieh, that really helped him connect a lot of the disparate pieces from the various practices he accumulated over the years and the Energy Arts system was put together in order to give some progression to help you awaken certain things.
Now all of that said... I would suggest doing the practice that resonates the most with your body and helps liven it. If the swings don't do it for you, don't keep flapping your arms around, that's not the point. If you find some other qigong that helps you really awaken your body, and feel the connection, keep doing that practice, and when you can consistently awaken that feeling in the body, try practicing Energy Gates (the swings or even just cloud hands) and then see how the practice works with your body in a different way.
It took a while for things to "click" for me, especially going off of books. As usual, the ideal method is to practice directly with BKF or one of his senior instructors. Even if you get out there only once, if you can really feel how its supposed to feel, that's going to get you much further much faster than trying to get it on your own (but it can be done if you are sensitive enough and don't easily self delude yourself, but if you aren't super self aware or familiar with other chi practices it can be hard to tell, so the safest bet is to take a trip to BKF directly or one of his seniors).
