1) first of all try to filter the search result according to seller rating, feedback and number of orders, the seller you mentioned above never sold this phone as feedback is null so avoid such sellers
> custom Duty for a phone is Rs250 flat rate but "custom walon ka kuch pata nai chalta" some times they charge more while sometimes they didnt charge anything
> you will have to get NOC from pta office islamabad
2) depends upon shipping method, if you select free shipping then either a postman will deliver it on ur door step or will call you to come to post office and collect the parcel after paying some chaye pani
3) you can pay either by credit card (master/visa) or westeren union.... CC is safe option
i suggest you to order low cost items first, in this way you will learn all the tricks of the sellers... and also the delivery process will be cleared to you