Hi, I am a graduate Civil & Structural Engineer working in a reputed company. I have an excellent academic & research background, so I can definitely help you here.
Hi, I have found answers for first two question. I will give answers for others If I am hired. ( With further research)
1). Yes, there is a limit to the maximum head due to practical issues. Typically maximum head that can be obtained is around 8-10 m from both pumps.
2). If you need to increase the output you have to increase the diameter. Larger the diameter, larger the output.
I have done 50% research at the moment. I can give further more comprehensive answers if you hire me. Looking forward for the job. Thanks