Is there any best practice how to deploy a multi-node BW on HANA system?
There is very good summary of scale out best practices in SCN put together by SAP's CSA expert group.
Is there a recommendation from SAP wether to use 512 GB nodes or rather 1 TB nodes?
Please have a look to OSS note 1855041.
Is there a way to automatically redistribute and partition data in a BW on HANA scale-out environment?
There is a automatic partitioning available for scale-out landscapes described in SAP Note 1908075. This can improve BW query performance.