If you are going to visit Gilgit/Skardu then do add around 2 more days...
My Suggestion will be to visit only one side at a time and explore it as much as you can... i mean only visit either Skardu or Gilgit don't add both of them in one trip of that small duration...
If you plan to visit Skardu then place to visit will be:
- Skardu.
- Shigar.
- K2 base camp and much more.
And if you are planning to visit the Gilgit region then:
- Gilgit
- Nalthar
- Ghizar District (Phundar and Gupis lakes are worth watching places)
- If you have some more time then add the Hunza valley in it as well.
For transportation, the most reliable medium will be to have your personal transport (either rented or owned)... and on second number comes the NATCO... not sure if it's working in this season or not...
If going on your personal vehicle, then from Manshera go via KKH avoid Babusar as it's closed due to snow...
But this is only my opinion... it could be changed as per your will power/stamina and resources... 