"I wrote a letter to Peter."
Translation:मैंने पीटर को एक चिट्ठी लिखी।
is word order strict? 'chitthi' -direct object - must be close to the verb?
Not necessarily. को marks the indirect object (Peter), and ने marks the subject (I), so even if you changed the order it would be clear that चिट्ठी is the direct object.
As far as I know, as a non-native but who has studied a lot of Hindi, that would not be considered proper Hindi.
However, in Punjabi (which I know better than Hindi), it WOULD be just "main". And since "Punjabi" language blends into a spectrum of languages until we reach "Hindi" of Delhi... I would not be surprised if spoken dialects of Hindi do the same.
Will be interested to hear what others say.