For what it’s worth, I would certainly echo the statements about avoiding any particular Wing Chun specific activity, such as forms etc, until you have been shown properly. The forms are so much more than a sequence of movements.
Even standing in the Kim Yeung Ma for periods of time is worth waiting until a qualified instructor can show how to to settle into the stance properly otherwise you risk training in bad-habits.
Once you’ve been shown things like punching drills, standing and movement drills, you can then train them in your own time to complement the partner training you’ll do in class.
For general fitness, any generic cardio or strength training will be of benefit but one aspect which is rarely trained (because it’s hard) is that of explosive speed/strength. For example, one training method I use is to alternate all out sprints followed by a light recovery jog. I use a football or rugby pitch but any patch of ground is fine. Sprint as fast as you can along the short end, jog or walk the long one as recovery and repeat. In time, sprint the long end and recover on the short.
Same thing for strength exercises - explosive clap pressups will do more for you than normal pressups.
Once you been shown basic striking techniques, try getting a partner to hold a large striking shield and just go all-out on it for 30 seconds. You’ll soon see how tiring this is. Then get the partner to move towards you, try to flank you or move away from you. The key is to keep the intense pace of the attacks for as long as you can.
Any martial art is not a game of top trumps (I have Wing Chun which beats your Taekwondo etc although you do see this kind of attitude). The art will require sustained effort from you (kung fu) to learn and master. Physical training is an aspect of this.
Also, where Wing Chun differs from certain styles is that it is not a sports combat art. In sports combat, the stylists will have timed bouts, rules and weight categories. Self defence arts do not. A self defence situation will be very fast and could be against an opponent who is a lot bigger.
But then again, it depends on what you want to learn Wing Chun for. Answer that question and you’ll know what kind of training you need to do.