Hi Daniyal,
Welcome to Pakistan and good choice to do tourism here.
-- From Islamabad, you can take the following route as shown in picture
-- There is nothing much in Kaghan itself but Naran has lots of places to see, if you have time, you can go to Shogran which is on way ( 8km from main road ) to Kaghan and Naran and you have to turn from a town called Kiwai, there is a place Paye, that u should not miss atleast...
-- Saif ul Malook lake is inside declared national park, so yes....
-- When u go to Lake Saif ul malook, you jeep driver allows you couple of hours to stay there and then u have to come back unless you have some special arrangements.
-- if u wanna try u can do hike to Lalazar, its gravel road with steep slop or u can hire a jeep.
-- Babusar top is very nice place and i suggest u should visit it too, take care its very cold and low in oxygen there.
- when u go there in Naran city there are hundreds of hotels so check rates with them and check other posts for hotel contact numbers pls