modify search topology

I have 4 app server. I have configured the service on server4.

I need to change the topology. I am following the Microsoft link to change the topology

The Script takes a very long time to complete and just hangs is this is quite common.

Do i need to run the script in parts and only create the new topology object after the search instance has started.

 $serverA="Server1"
    $serverB="Server2"
    $serverC="Server3"

$hostA = Get-SPEnterpriseSearchServiceInstance -Identity $serverA
$hostB = Get-SPEnterpriseSearchServiceInstance -Identity $serverB
$hostC = Get-SPEnterpriseSearchServiceInstance -Identity $serverC
Start-SPEnterpriseSearchServiceInstance -Identity $hostA
Start-SPEnterpriseSearchServiceInstance -Identity $hostB
Start-SPEnterpriseSearchServiceInstance -Identity $hostC

Get-SPEnterpriseSearchServiceInstance -Identity $hostA
Get-SPEnterpriseSearchServiceInstance -Identity $hostB
Get-SPEnterpriseSearchServiceInstance -Identity $hostC

$ssa = Get-SPEnterpriseSearchServiceApplication
$newTopology = New-SPEnterpriseSearchTopology -SearchApplication $ssa

#Server A
New-SPEnterpriseSearchAdminComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchCrawlComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchContentProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchAnalyticsProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostA


# Server B
New-SPEnterpriseSearchQueryProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostB
New-SPEnterpriseSearchIndexComponent -SearchTopology $newTopology -SearchServiceInstance $hostB -IndexPartition 0


New-SPEnterpriseSearchQueryProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostC
New-SPEnterpriseSearchIndexComponent -SearchTopology $newTopology -SearchServiceInstance $hostC -IndexPartition 0 


Set-SPEnterpriseSearchTopology -Identity $newTopology


Get-SPEnterpriseSearchTopology -SearchApplication $ssa

Get-SPEnterpriseSearchStatus -SearchApplication $ssa -Text