By default, only 60 tablets (partitions) can be created at table creation time. See the following limitation:
But you can add any number of tablets later on by adding range partitions once a table is created. (hash partitions will not be allowed to add after table creation)
so you can not create 120 partition during table creation, but since you need hash partition, so I suggest you create 20 range partition multipled with 3 hash partition (need to use primary key columns for hash partition), so in this way, you create a 60 tablets table, then after table creation, you can add more range partition by using "alter table" command from impala.
For the question about the number of hash partitions for a kudu table, there is no such formula, the purpose of hash parittion is just try to distribute rows by hash value and spread writes randomly among tablets, which helps mitigate hot-spotting and uneven tablet sizes.