Hi Pramar, I would definitely suggest a different trip for Spiti Valley. However, if you do decide to stay one night in Spiti Valley, I would recommend staying in the town of Kaza. Kaza is the largest town in Spiti Valley and has a good selection of hotels and guesthouses. It is also a good base for exploring the surrounding area.
Kunzum Pass Connects Spiti Route With Manali Via Atal Tunnel. Kunzum pass will be closed during November and December. So one can't go to Spiti valley via Manali or vice versa. It's better to made Spiti Tour separately during Summer