Hey Ravi, Himachal is a big state and you will need at least a month to cover all the state. Acc. to experiences you can follow this route: Chandigarh ->Trithan Valley (5 Days ) ->Mandi-Prashar Lake trek (2 Days) ->Parvati Valley-Malana,Kasol,Tosh,Kheerganga trek (5Days) ->Kullu-Manali(3 Days). You can go to Dharamshala-( Macleodganj, Triund trek, Dalhousie, Khajjiar ) after Manali. And for the activities 1)Rafting at Kullu 2)Skeeing at Manali 3)Paragliding at Bir (Dharamshala) or Kullu Happy travelling!!!!!!!!
Chandigarh - Shimla - before reckong take the cut from Karchham and do Chitkul- reckong peo- kalpa- Nako - tabo - kaza - chandratal - Manali winters full circuit of Spiti is not possible and only till kaza and back to Shimla