What decoder is a good fit for the HO scale Edward?
Where would one go to learn how to install it?
Pretty much any 'hardwire' decoder could be used. Space is limited, so I would suggest a decoder labeled as being for either 'N' or 'Z' scale, rated at least 1 amp.
These instructions are for Henry & Gordon, but Edward would be similar. They show a TCS decoder being used, but any brand will work:
http://www.tcsdcc.com/Customer_Content/Installation_Pictures/HO_Scale/Bachmann/Henrygordon/HenryGordon.htm
Len