Hey, your plan sounds interesting. From November onwards, Rohatang Pass near Manali will be closed for the travellers due to snowfall. So thtle only route to reach Kashmir is through Jammu. The route from Manali that goes towards Ladakh will be reopened next year (May 2019). You can take a flight till Srinagar if want to avoid the road journey from Jammu to Srinagar. There is one more route known as Killer-Kishtwar road which is not suitable for general public as it is very risky and especially during Winter season. You can easily visit Kashmir and Manali any time of the year. During Wnters (December-February) you will find snow). Have a safe trip!
You can visit till November. Because after November the roads can get closed anytime due to snow and landslides. There are two routes by which you can come to Kashmir. One is through Leh and another is through Jammu