The phrase "and if so how many" is correct and usable in written English. You can use it to ask questions or make a request for clarification when something is unclear. For example, "I heard there were ten guests at the party. Is that true, and if so, how many?".
And if so, how many are enough?
Will they want ads, and if so, how many?
Will people come and, if so, how many?
So should you eat more eggs, and if so, how many?
Are there dogs in your life, and if so how many?
It is unclear whether other sets of partial remains awaited similar burial, and, if so, how many.
Decision-makers must then conduct the necessary proportionality analysis: will civilians be harmed and if so, how many?
Thanks to Ludwig my first paper got accepted! The editor wrote me that my manuscript was well-written
Listya Utami K.
PhD Student in Biology, Bandung Institute of Technology, Indonesia