Impromptu - Leh/Ladakh plan

Carry a single backpack that can be tied to a bike. From Leh, ride to Nubra valley across the Khardungla —Hundar is the name of the place. You’ll get 50mpbs on Jio here, comfy stay so can be an alternate base from Leh to acclimatise. From Hundar, do overnight stay each at Turtuk and Stongstet near Siachen base camp (no internet at these places). These are remote places and may not have all facilities. I use booking.com but if you don’t find anything just reach there, ask around and figure a place to stay. I didn’t enjoy Pangong as much since the roads weren’t great but might want to tick that box by staying there overnight from Hundar and then returning to Leh — no internet though. Keep going along the lake and stay at the villages of Man and Merak to escape the crowd at Pangong. Altitude related problems can be expected at Pangong if not acclimatised well, so advisable not to ride alone. Other itineraries - Leh to Aryan valley to Kargil to Dras and back via Lamayuru (2-3N). This one’s more for cultural immersion, hearing Kargil war stories if that’s your jam. Kargil is a large town and can be a work station. Try the bread and cake from the local bakeries at Kargil. Apart from this, Zanskar Padum circuit is popular but haven’t been there and can’t comment.

You're going in off season so nothing will be costly, just beware of weather conditions- my flight was cancelled due to heavy snow at this time a few years ago (book the same airline if it's a hopping flight so you don't lose out if 1 flight is cancelled) For rentals, go to any shop and rent an Enfield/Avenger, they are fairly cheap and fun to ride in ladakh (roads are brilliant)

Best to book through thrillophilia or some other travel operator. They use a standard set of hotels and activities. 6-7 days is enough.