Advice on Cassandra partition and clustering key

I have doubts with respect to what should be the partition key and clustering key in the following two cases:

Case 1: Users can make multiple posts Queries:

1. Get post by id
2. Get all posts by user_id
3. Get all posts made by user_id where createdAt > X

If we have chosen the partition key to be post_id, then we can support only Query1. If we have chosen partition key as user_id (not very good as it can lead to imbalanced servers) then we can support Query 2 and 3 but not 1.

One way to support all the queries is by having multiple copies of data with different partition keys but that will take huge storage.

Case 2: Users make hotel reservations Queries

1. Get reservation by id
2. Get all reservations by user_id
3. Get all reservations by hotel_id

Is Cassandra the best choice for the above two data given:

1. Very high write throughput
2. Huge amount of data
3. No transactions needed.

Any pointers are deeply appreciated.