when i switched from isis (pixtools) to twain i found that there is no good free twain library (at least i did not find). for simple need this one:
is probably the best
also you can look into http://www.codeproject.com/KB/dotnet/twaindotnet.aspx
but at the same time you can find good paid lib like atalasoft .net twain and so on.
regarding your ADF/Feeder - it does not related to platform, open spec from this site and using tag you will be able to implement this within 10 min on any lib