You've asked two questions there.

> How much memory on block storage is required? Quite little, unless you also have performance requirements on the block storage. If you care about performance you'll want to ensure there's enough RAM that the block storage processes don't swap under production level loads.

> I am trying to ask if VM can utilize disk in my block storage and use 64 Gb memory on different compute nodes? No - a VM on one compute node may not utilize memory on anothre compute node.

I would recommend to provision that node as a storage node (only) - don't let it do compute, just storage. VMs on those other nodes (the ones with 64G RAM) can then remotely access the storage.