It depends your needs :)
What hazelcast does for e.g. a map is the calculate the hash of a key, do a mod partition count on it and that determines the partition the key will be stored on.
For a single node setup Hazelcast could make sense because the map provides more than a regular map, but its true value is with a multinode (2 or more).
We have customers that run with smaller clusters e.g. 5/6 nodes. Even with 2 nodes you still get certain features.
About the partition count: we aim that the partition size should be max 50/100 mb. So with 271 partitions you get +/13 gigs of data (50mb). If you would have 26 gigs of data, double the number of partitions.