Nice plan, let me add my comments inline to each point.
Just visited the same places last week alhamdulillah.
Quite cheap. But better to visit more hotels and try to negotiate after visiting room. Rent will vary from 1500 - 2500 if you will not go for very high lavish place.
Check for warm water, electricity conditions. Moon Restaurant in Main Bazar Naran is quite a good place for meal so don't need to bother for meal.
Yes, it can go easily. We went on our Mehran last week. Going from Naran towards Babusar and back is not that difficult so no worries insha ALLAH.
Didn't check it as we went on our ride.
Didn't hear any such issue. However, try not to drive in night as due to hilly area, it becomes difficult in night. We left Naran at ~1630 hrs and till after Balakot, it was bit dark and driving was not that easy and traffic was also increased. Especially, after Abbotabad, road is single with heavy traffic in night so better to avoid it.
Regarding your plan, I have a humble suggestion that try to leave early from ISB and reach Naran till 2pm (IA), then visit Saif ul Malook same day. It will save your time.
P.S. We did the same and it saved our time as well alhamdulillah.