Hey Nikhil. Delhi to Mumbai via Train would take atleast 19 hours. You can take bus from ISBT Delhi to Leh costing somewhere around Rs 1400/- but will take you atleast 40 hours to reach there. From Leh you canopt for a bike to Ladakh and monastery area.
Hey Nikhil, Duration for Ladakh trip: You need minimum 5 days in ladakh : Day1&2 : Local sight seeing ( Hall of Fame, Magnetic Hill, Leh royal Palace, Zanskar River Rafting, Shanti Stupa, Gurudwara Pathar Sahib, Spituk Monastery) Day3&4&5: Khardung La pass, Nubra Valley and Pangong Tso Rest depends on how you reach Ladakh from Mumbai.
a)Via bike from Delhi -minimum 5 days for Up and Down
b)Via jeep from Manali — 2 Days for up and down. Hope this would help you.