How can I merge this code so all stages use $RootPath?

I'm not a beginner to scripting with PowerShell and have discovered just how powerful and amazing it truly is. I get confused with some things though so I am here seeking help with a few things with the script that I'm in the process of creating. My script manages a few things. It:

• prompt user to select a directory

• recursively moves files that are many levels deep into the parent folder

• deletes all empty folders after the move

•renames the parent folders by removing periods and other "illegal" characters because the program that uses these files will crash if there are any characters besides numbers or letters.

• renames the files to the parent's name.

• exits when finished

The files don't have a file format extension, they're approx 32 characters long and are alphanumeric.

Unfortunately, the script cannot make it past the first step (moving the files) if it is placed in a directory outside of the one that contains the folders and files. If I place it in the root of the directory containing said files and folders, it works flawlessly. If it is ran in another directory containing other files, it will work with the files and folders there after finishing the 1st step which is set using $RootPath, the rest of the script is not using $RootPath and I need to figure out how to edit the code I have to utilize it.

However no matter what I do, I fail. I know I can just run it from the directory containing the files that need to be moved but I intend to release this on a forum that I frequent and want to make sure it is safe for those that use it. ie: I don't want their system getting messed up through carelessness or ignorance.

Full Disclosure: I'm not good at writing code on my own, I find chunks of code offered in forums, test and if it accomplishes what I need, I tweak it to work with my intended use. Most of this code I found here.

How can I get the last ⅔ of my script to use my $RootPath instead of the script's residing directory? I have tried a few things but end up breaking it's functionally and the thing is, in my mind, I see why it's not working but reading the code is where I have a Patrick-Star-drooling moment. This is when I get overwhelmed and take a break or focus on something else that I do understand. I know I need to make the rest of my code utilize $RootPath that gets set when selecting a directory but I can't figure out how to get it to use it.

Additionally, I would like the final step to append "_1" to the file name when there is a naming conflict. I can't seem to figure out how to get this step to carry over from the first step.

Here is a pastebin link of my script. It is a bit long, I have also pasted the code in case that is preferred.

# You need this to use System.Windows.MessageBox
Add-Type -AssemblyName 'PresentationFramework'
Add-Type -AssemblyName System.Windows.Forms
 
$continue = 'No'
$caption = "'Bulk File Renamer Script' by MyLegzRwheelz."    
$message = "Have you read the ENTIRE disclaimer (from the very top, I know, it is a lot) in the console window along the instructions provided and do you agree that you are responsible for your own negligence and anything that can go wrong IF YOU DO NOT FOLLOW MY INSTRUCTIONS PRECISELY? If so, then click 'Yes' to proceed, 'No' to exit."
$continue = [System.Windows.MessageBox]::Show($message, $caption, 'YesNo');
 
 
if ($continue -eq 'Yes') {
$characters = "?!'._" # These are the characters the script finds and removes
$regex = "[$([regex]::Escape($characters))]"
$filesandfolders = Get-ChildItem -recurse | Where-Object {$_.name -match $regex} 
$browser = New-Object System.Windows.Forms.FolderBrowserDialog
$null = $browser.ShowDialog()
$RootPath = $browser.SelectedPath
 
# Get list of parent folders in root path
$ParentFolders = Get-ChildItem -Path $RootPath | Where-Object {$_.PSIsContainer}
 
# For each parent folder get all files recursively and move to parent, append number to file to avoid collisions
ForEach ($Parent in $ParentFolders) {
    Get-ChildItem -Path $Parent.FullName -Recurse | Where-Object {!$_.PSIsContainer -and ($_.DirectoryName -ne $Parent.FullName)} | ForEach-Object {
        $FileInc = 1
        Do {
            If ($FileInc -eq 1) {$MovePath = Join-Path -Path $Parent.FullName -ChildPath $_.Name}
            Else {$MovePath = Join-Path -Path $Parent.FullName -ChildPath "$($_.BaseName)($FileInc)$($_.Extension)"}
            $FileInc++
        }
        While (Test-Path -Path $MovePath -PathType Leaf)
        Move-Item -Path $_.FullName -Destination $MovePath
    }
}
 
 
$filesandfolders | Where-Object {$_.PsIscontainer}  |  foreach {
    $New=$_.name -Replace $regex
    Rename-Item -path $_.Fullname -newname $New -passthru
}
 
# For this to work, we need to temporarily append a file extension to the file name
Get-ChildItem -File -Recurse | where-object {!($_.Extension)} | Rename-Item -New {$_.basename+'.ext'}
# Removes alphanumeric subdirectories after moving renamed game into the parent folder
Get-ChildItem -Recurse -Directory | ? { -Not ($_.EnumerateFiles('*',1) | Select-Object -First 1) } | Remove-Item -Recurse
# Recursively searches for the files we renamed to .ext and  renames it to the parent folder's name
# ie: "B2080E9FFF47FE2DA382BD55EDFCA2152078AEBD58.ext" becomes "0 day Attack on Earth" and will be 
# found in the directory of the same name.
ls -Recurse -Filter *.ext | %{ 
    $name = ([IO.DirectoryInfo](Split-Path $_.FullName -Parent)).Name
  Rename-Item -Path $_.FullName -NewName "$($name)"
}
    
} else {
   {Exit}
}

I have tried using $ParentFolders in varying places so that it uses $RootPath as the working directory. I have also tried copy/pasting the "file inc" part in the final step but it is not working. To test this out, create folder, make this your root folder. Within that folder, create additional folders with multiple subfolders and a file with no extension, just create .txt and remove the extension then run the script from the newly created root folder.

Do not run this in a directory with files you care about. This why I am trying to get the rest of the code to use only the directory set at launch. To test it to see if it is working regardless of the scripts location, place the script in another folder then run it. When the explorer dialog pops up (after clicking yes), select this directory. If you place it in the root directory then run it, it works as it should but not in any other director, which is the desired result, to run and work to completion, regardless of the location of the script.

Here is code to add _1 to filename

<!-- begin snippet: js hide: false console: true babel: false -->

$filename = "abcdefg.csv"
$lastIndex = $filename.LastIndexOf('.')
$extension = $filename.Substring($lastIndex)
$filename = $filename.Substring(0,$lastIndex)
Write-Host "filename = " $filename ",extension = " $extension
$filename = $filename + "_1" + $extension
$filename

<!-- end snippet -->