I'm planing to re-factoring our client's Models as some Models have over 100 modules which is not easy to maintain. Please advise how many modules should be in one Model in general.
100+ modules, in and of itself doesn't sway me one way or the other. In most models, regardless of the number of modules, there are a handful of workhorse modules containing the most complex logic (or otherwise taking up the most space and/or resources). Therefore, the number of modules isn't determinitive.
I typically will separate (an activity or activities) into separate models based on the following factors (in no particular order):
Let's see what others have to add!
The number of modules is not the primary design feature to solve for. Focus on useability and the overall manifesto of the use case. Be especially aware of redundancy and inefficiencies in modules which negatively impact performance and user experience, i.e. don't repeat module structures (line items).