DS1621+ & TS-832PX which one is better in my case

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DS1621+ will be a good choice. Qnap might require more configuring which also might be more complicated. Synology will do a better job guiding you through the process of securing your NAS. But both systems can be configured to be safe.
People only need 10GbE for video editing most of them time. Others are happy with 1GbE.
Having 4GB RAM is enough.