Just to be clear, is your sole reason for wanting to do this because of the high datastore activity that concurrent clones generate?
Yes, that is the main reason. It also makes the monitoring logs easier to follow for me without having to filter for individual machine names.
By default vCenter supports 8 concurrent operations. vRA by default supports 2 concurrent provisioning. If you want to change the default provisioning from 2 to someother value after taking into consideration the endpoint[vcenter in this case] can handle it then you can change it accordingly. More details over here
I found a decent workaround to accomplish this. I fired off a deployment with 1 machine and then afterwards I used the scale out feature to add more machines 2 at a time. This worked well for me. It was also nice when a scale out request failed, I was able to just fire off another one while keeping the main deployment in tact. If I had deployed all instances at once in a single request and one of them failed, the whole deployment would have been destroyed.