Need help regarding power source for a 60V BLDC motor
If you have 5 batteries in series, you will have 60V at 7.5 Ah. If you have 5  batteries in parallel, you will have 12V at 37.5Ah. You cannot connect them in series and parallel simultaneously.

I would like to introduce you to the concept of energy. The energy in a battery is approximately equal to the voltage * capacity. So each battery has 7.5Ah * 12V = 90Wh. With 5 batteries, you will have 5 * 90 = 450 Wh. This is the energy content of the batteries. It cannot be changed by re-arranging the battery connections.

With 450 Wh, you will be able to supply 1000 Watts for maybe 10-15 minutes. In theory it would be 450Wh / 1000W = 0.45 hours = 27 minutes. But in the real world, you cannot get full capacity from a lead acid battery if you discharge it rapidly.

Also please note that motors are often rated by output power. A motor that puts out 1000W of mechanical power will likely consume 1200W of input power. So that makes it even worse. It is hard to get efficiencies higher than 85% or so in small motors.

However, based on my knowledge of things like e-bikes and other personal electric vehicles, I would say that a 450 Wh battery should be able to propel a very lightweight vehicle for 1 hour at a modest speed. Faster than walking. Maybe jogging speed.