Firstly sorry about the late response. Hectic two days.....
So my advice goes as follows:
Its going to be your first time up there. You have way too much to see. So dont limit your self by a trek. I promise you that just a drive to any one of these places will leave you overwhelmed and intoxicated. You do not need any trekking. You have 10 days in total (3-4 possible trekking days) at max, dont spend them battling up a mountain pass or through a valley when this is the first time you'll be there. Id rather have you travel and see as much as is possible than just a single mountain or valley, especially when the sights along the road are no less spectacular than anything beyond the track. Trust me, you will have all your senses overwhelmed and overclocked. I have traveled twice to Skardu and once to Gilgit just for the sake of traveling on that road. Due to time constraints I didn't stay a full day on any of those trips. Mind you, any trip up our north is as much about the drive as it is about the destination.
I suggest that you start off with the classical/original KKH route. Dont turn right from Mansehra towards Balakot/Naran/Babusar, instead keep following the KKH straight to Badgram-->Behsam-->Patan-->Dassu-->Chillas. All these towns have good accommodation (PTDC and/or other motels). The route is extremely beautiful. From Chillas onward the mind blowing magic starts. From Chillas keep on riding the KKH. You will pass through the edges of the Babusar and Diamir valleys. Here you'll reach the Nangaparbat viewing point and pass along the Raikot bridge. Keep going straight on to Jaghlot-->Gilgit-->Karimabad. You will pass through the point where the three highest ranges of the world meet. And from here onward you will be mostly traveling in the Karakoram. In Karimabad stay for a day or two and explore the surroundings. This town alone is spectacular. There is loads and loads to see here with many one dray treks available too. Just from the town you'll be able to see Rakaposhi (7788m), Ultar (7388m), Diran (7257m), Spantik aka Golden Peak (7027m) and Bublimating Peak aka Ladyfinger (>6000 meters). The Baltit fort and the Eagle's nest are two places here which give an epicly amazing panoramic view of the Hunza valley. They are a must to visit and I strongly suggest that you do. Many day treks available here e.g. you can trek to the famous Ultar meadow. The trek takes about 7 hours round trip (4 hours there and 3 hours return). It can be easily done as a day trek. The ascent is rather steep, up a very rocky path and route is not very obvious, so do ask the locals for the correct direction but you shouldn't need a guide even though having one would be better. This trek will give you some really close views of Ultarsar and Ladyfinger with good trekking fun.
From Karimabad instead of going further north come back to Gilgit. You can stay here and go on any of the day treks available here but I suggest you instead start towards Skardu. A little south from Gilgit you'll turn east on the Gilgit/Skardu road from Alam Chowk. The Nangaparbat's north face will greet you on you right side as you climb up. The drive from Gilgit and Skardu should take you around 7-9 hours and I seriously suggest that you make during the day. This stretch of road is phenomenal and is something you do not want to miss in the dark. Very very high and very very steep mountains clad in ice and snow with
EXTREMELY narrow valley down bellow. This road introduces you to the Karakoram. Jet black, unimaginably steep and high rock faces
right besides you while you are travelling hundreds of feet above the river in a very very narrow valley. This is my favorite road in the world! You will pass many different little towns along the way but no noticeable motels. In Skardu stay a day or two. Go see the Skardu desert, climb up to the Skardu Fort, check out the Sadpara, Upper Kachura and the Lower Kachura (Shangrila) lakes. Can go on many day treks here too. Loads and loads to see here (even more than Karimabad). From Skardu you
must make your way further east towards Siachin. Skardu-->Ghanche-->Barrah-->Khaplu; I will not state how amazing and beautiful these places are because, firstly, that goes without saying and, secondly, you might think that im a blabbering buffoon. When you see them you will understand too
From Khaplu I strongly suggest that you jeep your way north to the Hushe village in Hushe valley (Desperately trying to hold my self from starting off about this place too). Famous peaks like Masherbrum and Laila Peak visible from here. The time you'll take from Skardu nonstop to Hushe is around 5-7 hours. But I promise you that you wont be going nonstop
Then drive back to Skardu. From here go south passing through Sadpara and from right besides the Deosai planes onto Astore. But before setting off do check if the road is open. This track takes some very heavy snowfall every season.
Check out the Astore valley which should be completely white (Its already snowed 2/3 times there this winter). From Astore ride the Astore road north-west to reach the KKH again. You will reach the KKH around the point where you first saw Nangaparbat. From here make your way back south. Now if you dont have time continue back to Chillas but if you do then stop when you reach the Raikot bridge, cross it and take off on the Fairy Meadow road. Spend a night or two at the Fairy Meadows and then make your way back to the Raikot bridge. When you reach there go on south to Chillas.
Now from Chillas, instead of following the old KKH route back (The way from which you came), take the new road going towards Babusar. You will first have to check with someone in Chillas if the road is open. This road is usually closed off dureing the winters due to excessive snow fall. This is going to be the new KKH route in the future. You can go up the Babusar Top which presents an amazing view of the Babusar valley and Nangaparbat. Then continue onward and if you have time you can go up and check Lalazar and the Dudipatsar lake out but only if the road is passable. The road from Babusar valley will take you past the Lulusar Lake onto Jalkhad. Then its Jalkhad-->Batakundi-->Naran. In Naran you can spend a day and go see Said-ul-Malook. The lake should be completely frozen with zero annoying tourists anywhere. From Naran-->Kaghan-->to the foot of Shogran. You can go up and check Shogran, Siri and Pai out but I doubt that the roads would be open at this time of the year. From Shogran you will make your way back to Mansehra thorugh Balakot and then to Abbottabad and so on.
After that you will spend each and every passing day of your life remembering this trip and wanting to go back the first chance you get :p
Good luck bro! You will have unimaginable fun. I wish I could have two years and enough money just to go to G/B and explore it as much as I can. Something which very little people know is that any trip to these places is like a 'reboot button'. You always come back a different person, a better person with not a care in the world and a deeper and happier view of life and the world.
Take loads of pictures when you go. I plan to open a thread just about the trips to G/B of our members very soon. I have gazillions of pics to share