Is there a list of diacritic signs in Hindi? Are the diacritic signs written only after or before the particular letter as well? I am developing a touch typing tutor http://www.typingstudy.com and I want to develop it for Hindi as well.

Wow, that is quite an undertaking. Devanagari diacritics are typically placed above or below the affected "sound". There are a number of very informative websites out there.  I found this one:

http://hindilanguage.info/devanagari/

But I am guessing there are loads more. Ideally, find a Hindi speaker (despite working in India on and off for years, I never learned the language. Lazy Englishman!),