Residential Plot In E/12 Sectors In Islamabad

I would be grateful if any respected senior member can tell me that if I purchase a plot in sector E12/3 with area of around 4.5 Marla (25x40) without possession letter from the owner through a reputed estate agent in Islamabad will it be legally okay or no.

Also can I sell it without any problem and in profit in future if the possession letter is not issued till the time of sale.

What is the price range in sector E12/3 for a plot of 4.5 Marla (25x40)?

Thanks

Dear brother U can purchase a plot ib e 12 3 but without posession as its not a developed sector So before buying any plot in e 12 please check it fron cda one window