The long fist system is a good starting point for all MA training. If you know how to transfer from one stance to another stance, it's very easy to learn any MA system after that.As for Long Fist before Taiji, I can see it could help, but my Taijiquan Shifu would likely not agree and he has been at taiji and only taiji for well over 50 years
The Taiji system original came from the long fist system. Even today, Taiji long fist still exist in both Yang and Chen.