The (optional) is added to the interface automatically when you specify that the parameter is optional so it really can't be avoided.
You can set all fields as required but default the values to something:
Then in the tool if the value is default or nonsensical (not found in file system for example):
import arcpy, os, sys
Oparam = sys.argv
# value found, assume it is a correct value
# value not found, assume it's skipped
Your best option for invalid values is arcpy.Exists which returns true if the data exists as an Esri type, files and folders can be checked using os.path.exists and either of
os.path.isdir() to validate if it is a file or directory respectively.
Otherwise you can create your own custom form in C# or VB.net and use the IGeoprocessor interface to run the tool. I don't recommend this as you can't list it with the tools in the toolbox.