I would develop software using C#.net windows forms.
Antivirus is bit difficult but possible for me. Cleaner functionalities are easy to develop because I am working on same project.
I can provide a ready antivirus ESET NOD32 Antivirus 6.0 with a key for a year or we will agree.
Options are possible: the portable version, updates without key in the form of the batch file (cheaper)