The SSDs you linked are the ones I put in my R5. I use the Crucial SATA SSDs for storage. I have also used this M.2 PCIe adapter  in another Dell rig if you want to add a M.2 SSD in a PCIe slot. Depending on your usage regime, I am not sure how much difference the reads speeds make in everyday 'normal' applications.
My current config is 512GB M.2 PCIe NVMe SSD (Boot) + 2TB 7200RPM SATA. I need at least a 1TB SSD now. From what I understand, I can't add a second M.2 SSD drive because there is only one slot M.2 slot used by the existing SSD drive. So, if I replace my existing SSD I need to clone it to the new one. That doesn't sound like fun... I also believe I can add a SATA 2.5 SSD to one of the existing, empty 2.5 slots that I have, using one of the available SATA drive connectors (#18 & #19 on the System-board components diagram). Do I need to worry about performance loss here? I am just now learning that there are multiple connectors for SSD drives (I'm a software engineer, I don't have to think hard about hardware lol). There also appears to be M.2 -> PCIe adapters that I can use if I want to use up one of my PCIe slots instead? But I'm not sure, I'm starting to get lost with all of these options. Which is the best upgrade path?
Area-51 R5, SSD upgrade options