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 what node size works best for a BWoH scale-out system?
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. Please make sure to review OSS note 2019973 which explains in detail all best practices around dealing with large data volume tables!
There is also a How-To paper about configuring SAP HANA Table-Distribution for BW-on-HANA Scale-Out Systems.