I noticed that with this script the Farm account gets used as teh Default content access account even though the Pool account gets properly configure. Maybe it is something specific to my configuration, but I am pretty sure you don't want the Farm Application Pool account to be the default content access account. Also: I am guessing since the Default content access account is not a managed account, you probably don't want to use managed accounts if they are going to have scheduled password chanages. Any comments or thoughts on how to do this differently so that a different search account is used for the Default content access account would be greatly appreciated.

Found this script on MANY blogs and in Wrox book, but "New-SPEnterpriseSearchAdminComponent..." commands after #Configuring Search Component Topology always fail with my SP2013 install.  Do you know what the proper commands are?

What is the error when the New-SPEnterpriseSearchAdminComponent command fails ?

thanks for the amazing article it worked for me except the DB name is not correct , instead of "DatabaseName = "Search15_ADminDB" " it adds DB as "Search15" and give this error.
-DatabaseName : The term '-DatabaseName' is not recognized as the name of a cmdlet, function, script file, or operable program.
Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:29 char:1

also how to make sure that search working properly, as i have add start address on the Content Sources, and run full crawl, however, not able to get a search result

lol, your error is that the line in the script beginning with -DatabaseName is actually a continuation of the previous line... put it back up there and it should work.