Optimum activity numbers in project for best schedule

i m working Engineering Management and Consulting Services and we are consulting iron and steel works companies modernization projects.

we have scheduled all projects with ms project and when i finished schedule of a modernization project. approximately i have 4000 or 5000 activity in my schedule.
i m sure that, too many activities are not focusing the critical path cause of many kind of different works in a project.

i’ve seperated civil construction works, mechanical erection works, bidding and procurement works and electrical-automation works from my first schedule, and i wanna assamble one master schedule from these programs but i cant use the external task or ghost.

anyone have a idea about optimum activity numbers for the best critical path or what is the optimum detail for a project