The default is for 32 and is controlled by the das.perHostConcurrentFailoversLimit option. More information on this is found here: Advanced configuration options for VMware High Availability in vSphere 5.x and 6.0 (2033250) | VMware KB
For my 2c worth I wouldn't change the default as with 10 ESXi hosts in your cluster and if you assume a single hosts fails, this gives you up to 288 VM power-on attempts. Given the numbers you have specified below of ~30 VM's per host with the defaults this would be happily serviced by 1 host without worrying about the other 7 hosts.
Hope this helps.
Thanks for replying
You mentioned """this gives you 288 power on attempts"""" I understand this value comes from 32 vms can be powered on at once and I have 9 Hosts i.e. 32 * 9 = 288
Please help me understand as per the article you mentioned das.maxvmrestartcount is 5 i.e. a esxi host will try to power on a VM for five times only after which it will not power it on. so this means that VM will get only 5 power on attempts how will 288 attempts help here
I am unable to understand how will 288 power on attempts help
Short answer is it will not - the das.maxvmrestartcount is the amount of times a single VM will try to be started in a HA event before the FDM master gives up.
My wording might have been slightly misleading in my reply. Perhaps I should have said that with the default value for das.perHostConcurrentFailoversLimit you will get up to 288 VMs trying to power on concurrently based on an assumption of 9 surviving hosts. Sorry that this wasn't as clear as it should have been