Hello Lorna, it's interesting to hear that you are trying to grow cacao plants. Unfortunately the cacao trees are very sensitive and require specific geographic and weather conditions.
The good news are that with technology we have been able to recreate such conditions for the trees to grow strong and healthy. In regards to the height, it is not really important, the height will be dependant from the variety that you are growing.
I have some good information about planting, growing and harvesting cacao but most of it is in Spanish. I consider this two links will be very helpful for you, take your time to review them
This includes all what you need to have high quality cacao beans (in recommended conditions).
I also have a little cacao tree. I haven't had it long- probably 2 months. We haven't really given it enough attention and it's not going so well. It's about to get really cold here in South Australia- was wondering if anyone has any tips to keeping it at the right temperatures and humidity… Should I just buy or build something to house it in and keep it at the right conditions?