PCI6602+Qt

I am using Qt and PCI6602 for edge count. I am using an external clock which is 4Mhz. The code is:

step 1. DAQmxCreateTask("",&newtaskHandle);

step 2. DAQmxCreateCICountEdgesChan(newtaskHandle,"Dev1/ctr2","",DAQmx_Val_Rising,0,DAQmx_Val_CountUp);
step 3. DAQmxCfgSampClkTiming(newtaskHandle,"",4000000.0,DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,bufferlen);

step 4. DAQmxStartTask(newesttaskHandle);
step 5. DAQmxReadCounterF64(newesttaskHandle,1024,10.0,inputdata,1024,&read,NULL);
step 6. DAQmxStopTask(newesttaskHandle);

It takes 2ms from step 4 to step 6.

Now, I want to synchronously use eight counters, ctr0-ctr7. Each counter reads 1024 samples.

My question is:

1. Is it possible that I synchronize the eight counters on PCI-6602 and How to do this if this is possible?

2. What is the Maximum external clock ? 

3.  How can I reduce the time from step 4 to step 6?