Saleh, that is a good option but you should/must have another option in mind, Top City and MPCHS B-17 can be two good options.
Hammad Arif, I think Bluebell is the best block for Commercial Investment.
Valley prices are stable in the blocks which are in the start Blubell, Rose, Tulip, Daisy are considered good blocks, Lilly and Orleander are considered good as DHA Homes are in these two blocks and development is underway.
Possession can be given in 4-5 years, but i think DHA will give possession in parts, They have to give possession for DHA homes, then may be they have to give possession Lilly, Orleander and Bluebelle, later they give possession in Lotus, Lavender and Iris block which are far behind, and then the remaining blocks, plus Overseas blocks.
Valley is not a bad investment considering in mind the plot prices in Islamabad/Rawalpindi.