I was happy to see that you had 4X5 equipment because masking is more easily accomplished with the larger negative. However, it can also be accomplished with medium format negatives. Since you indicate a familiarity with unsharp masking, that then leaves sharp masking of various types and effects as the next course of action. As I had mentioned this is where precise registration of the camera negative and masks comes into play. The reason for the need of precision is that there are many times where several mask changes involving removal of the negative carrier from the enlarger and reinsertion with a new mask and additional exposures are the course for accomplishing one's desired result.
Unfortunately, this then brings us back to a need to accomplish this precise repeatability through modifications to enlarging equipment. My modifications to my enlarger system involve a film punch that is registered with a mask printing frame and these two componants are also registered with the negative carrier of the enlarger. The negative stage of my enlarger was modified to provide for repeatable positioning of the negative carrier after each removal and reinsertion. My modifications cost several times what Lynn Radeka charges for his newer system. As I mentioned before, I don't have any opinion on his system (hardware) since I have not used it.
If you are interested in pursuing this further (beyond unsharp masking) then these issues must be addressed. Possibly if you could indicate your enlarger manufacture and model that may be a place to begin. It may very well be that Lynn Radeka's newer system is what would be best for you. This may be a time for further evaluation of the level of your desire.