PTDC transport is good for Naran. No need to hire private transport if your plan is just to visit Naran.
Weather in Naran is 0 at night these days. During day time max is 12. As you are coming from Karachi, so it will be cold for you. Come well prepared.
Jeep to Saif ul Malook can be booked for 1800 these days. Don't pay more than that, no need to visit Siri Paye, not worth the hassle.
Why Murree? don't spoil your trip by going to murree, it was good 20 years ago. Galiyat is better than Murree.