Hi Ianmac,
I have similar project as yours, it became huge file and takes time to open. Since other application modules need not to open everytime by the user, I have broke it up to several apps. I use 'shell' to open them in background. Some of my apps still takes time to open. It will be faster once Basic4ppc version 6 is released.
See this thread for reference...
Getting value from other other application in runtime
We could ask other members what other method could be done.