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SPK Network PoA mainnet. For now hive rewards will suffice

Could be done via reward.app delegation for liquid payout? a setting in the .env like: liquid-rewards, yes or no

Regarding the Storage - Is it ok to have just HDD Storage on a Server or does it need to be SSD Storage which would be then a solution for a custom pc / work server at home.

Could be done via reward.app delegation for liquid payout? a setting in the .env like: liquid-rewards, yes or no

Good idea! Will make note of it!

HDD server is fine. For larger setups with multiple drives I'd suggest using ZFS with SSD caching. The more IOPS the better typically, but you can get away with lower end setups since this is all backup storage anyway.