Let me simplify this and assume that you are OK with selecting a folder when the script runs. For this you can use a 5-step workflow:
Step 1: Set Value of Variable

This captures the files passed into the script and stores them in a variable, so we can refer to it later. I called the variable FilesToMove, but it could be anything you like.
Step 2/3: Prompt for folder

This is a two-step process with some very specific settings.
First is a 'Ask for Finder Items' action. This posts the standard 'choose file' dialog for the user to select a folder.
The important settings here are:
a: Start at - set this to your Modeling folder. That way when the dialog opens, it is already set to this location (my example uses Desktop because I don't have a Modeling folder)
b: Type: Folders - this ensures that the user can select only folders.
c: Options: Ignore this action's input - this is essential otherwise it will merge this action's result with the previous action (the list of files to move) and bad things will happen in that case.
Note that because this action uses the standard Open File dialog, it is technically possible for the user to select any folder on the disk. It just defaults to the Modeling folder to make it easy for them. If this is a problem we can look at other approaches.
Once the user has selected a folder, the second part of this step stores that result in another variable (in this case named subfolder but it could be anything you like.
Step 4 retrieves the list of files from the beginning of the script using a simple 'Get Value of Variable' action:

Important parts here are:
a: Identify the variable you used to store the files from the beginning of the workflow
b: under Options, turn on Ignore this action's input, otherwise we'll have the same problem as before, where it will try to merge the two variables.
The value of the variable (i.e. the files to move) are passed into:
Step 5: Move the files

Here, the Move Finder Items action expects to be passed in a list of files to move - we just established that via the Get Value of Variable. The kicker here is that you set the To: parameter to the variable you used to store the user-selected folder. This isn't obvious, but when you use the 'Set Value of Variable' you'll see a list of variables at the bottom of the workflow window. Just drag your variable to the To: field (it's non-intuitive) and you should be set.
Hope that helps.