Please try to first fix the issue of correctly naming images for corresponding channels.
In your module Metadata, the regular expression was not set correctly to the names of your images, e.g. A01fld1DAPI
You can actually skip that Metadata module (Extract metadata : No)
Then in you module NamesAndTypes
Make "File__Does___Contain__DAPI" = DAPI_channel
Make "File__Does___Contain__FITC" = FITC_channel
After having correct DAPI image named "DAPI_channel", FITC image named "FITC_channel", etc. >> in your module IdentifySecondaryObjects : choose "Select input image" with "FITC_channel", then the total actin area of the cell will be identified correctly.
You may find some good advices from Beth here
As for : "Is it possible to merge two and or more images"
Yes, we have module called ImageMath in which you can choose the operation Add to make the merge.