You have to rename your files two or more times to get all this request solved.
Best make an backup first, and test the use of BRU with some sample files!
I'm looking for a regular expression that deletes all characters ($, %, & etc.) from the filename.
The only characters that are allowed are a-z and 0-9.
That didn't work with BRU regex function because you have to match the whole string always, not only single signs.
Instead see what Remove(5) can do for you:
D/S: remove double spaces
Sym: remove symbols like !$&,-_#
Chars: [ your list of signs to remove ]
Spaces should be converted to _ (underscore)
Replace: [ ]
Replace an blank with underscore.
Don't use this together with "Remove(5) Sym:[X]" enabled