Go with option A) Chilas - Jaglot - Skardu, if you directly want to reach Skardu.
Stay at Astore (try to get pre-booking) if you want to opt for 'route B', i.e. via Deosai. Pros: adventure, beautiful, more lakes. Cons: Take good performance 4X4, carry extra fuel, if can't find room be prepared for camping in cold night.
For your last question: Visit Khaplu and touch Shigar dessert on the way, if still got more time than do Shigar fort trip!
If you decide to go with 'route A' go to deosai from Skardu, if its 'route B' stick with fort visits.
When do you leave? Safe travels
Regards,
Salal Abid