I made some updates to the Flex-Rig Assets:

• Split the clothing to Top, Bottom, Tie and Shoes. This gives me more flexibility to select the combination I want
• Added more clothing (and in the process of adding more)
• Created a few more Characters to use in the Open Movie Project

I'll be uploading the update in the next while, as I'm still cleaning up the file.

I wanted to share here the steps to add your own clothing assets to the characters:

• Steps to add Clothing
  • Design the clothing (or get them from some where). I found fuse to have a nice library of clothing
  • Use the base character to fit the clothing
  • Make sure to Ctrl+A (Apply transformation)
  • Parent the clothing item to the armature
  • Transfer the weights from the model to the clothing item
    • Select the mesh with the weights (the body of the character in this case)
    • Select the target (the clothing item in this case)
    • Go to weight paint mode
    • Weights (menu item) -> Transfer weights
    • Use "by Name"
  • Transfer the shape-keys from the character to the clothing. To do that we need an add-on (Shape Key Tools) - I have made some modification to this add-on which aren't published yet.
    • Select the source mesh
    • Select the destination mesh
    • Copy the list of shape keys by using the "Copy Shape Keys" button
    • Remove any unneeded shape keys. In my case its the face shape keys as they don't really apply to the clothing
    • Paste them back in the list of shape keys to transfer using the "Insert Shape keys" button
    • Hit the "Transfer Listed Shape Keys". This will transfer the shape keys to the clothing
  • Do any required cleanups
    • Hit the transfer drivers from shape keys
    • Copy the drivers on the shape keys
    • This will require modifying the add-on to copy the driver from each shape key and then add it to the copied shape key
    • Drivers are needed so the clothing can follow the modification in the body variants
  • Modify the pose_bones['body_variants']['clothes_top'] and pose_bones['body_variants']['clothes_bottom'] to account for the new clothing
  • Modify the driver on the mask modifier invert button so that when the variable is set to whatever specific value make the clothes appear or disappear
  • Modify the mask drivers on the model to make sure that they kick in when the clothes are selected.

Depending on time I might do a video tutorial on this