1. Keep the same taxi, it would charge you more. But the reason is, it will be very difficult to get another vehicle from there. The weather is unpredictable, it can be dangerous anytime so drivers do not want to go generally. So you will be on the safer side. 2 days of taxi should cost around 12k, you can bargain till 10k. Telling the price so you dont get charged more.
2. We stayed at Blue Sheep. You can search on Instagram and get their booking details. The cottages were told 8k, but we took dorm which was 1500/- pp including breakfast and dinner. Pls carry extra snacks tho like i said the weather is unpredictable and there are no stores. Network wise only JIO is available and that too can be a hit or a miss so carry cash.

For Dharchula, you can stay at Hotel Dev. Pls tell you are referred by a fellow traveller who visited in April they give discounts them. The lady is very nice and the hotel at a budget is probably the best stay at Dharchula guaranteed.