What NAS would work for me

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When it comes to considering the DS1522+ for your needs, it's understandable that you have concerns about the compatibility of NVMe and RAM options listed on Synology's website. They tend to promote their own branded components, which can be quite expensive. For instance, the price doubles while the NVMe cache size gets halved. However, it's important to note that you're not limited to sticking with Synology alone. As you mentioned your main purpose is movie storage and streaming, Plex app usage, containerization experimentation, and even hosting for friends like a Foundry server, there are workarounds available. Knowledgeable users have discovered ways to change the settings on Synology devices to bypass the warnings associated with third-party drives and SSDs. They have also successfully enabled NVMe pools with non-Synology SSDs. So, even if you opt for third-party components, they can work effectively; you just need to disable the warnings and make the necessary adjustments. By exploring these alternatives, you can avoid the hefty price tags attached to Synology's proprietary hardware and find more cost-effective solutions without compromising on performance.
Alternatively, go for Qnap TS-h973AX or a similar NAS.