First of all if you seach this forum you will find hundreds of threads relating to Kaghan valley. You will find all your answers there.
Second of all, it seems that the vehicle you will be traveling in is really not mechanicaly sound (otherwise you won't have so many apprehensions). I would suggest either you find a more mechanicaly sound vehicle or you switch your plan to public transport. Believe me it will save you a lot of hassle and money. Mechanics after Mansehra are not readily available, and those who are available are mostly diesel (jeep) mechanics.
However, if you still want to take your vehicle up the valley, then i suggest you invest in a good quality tow strap and a flash light, because that will be the only option vailable to get your vehicle out of the valley or to a workshop. I would also suggest for you to allocate an extra budget for such an emergency (you will need it).
Hope this helps.