The Dell Precision 3630 has 2 PCIe physical x4 expansion slots.  Since the slots don't have more than x4 lanes, there's no point in trying to use any PCIe cards with more than one M.2 NVMe SSD on it, since M.2 NVMe SSDs need x4 lanes to get their peak performance.  Assuming both slots are electrically x4 lanes and PCIe 3.0 for max performance, you could potentially add 2 more M.2 NVMe SSDs via (2) add-in PCIe cards in addition to the M.2 slot directly on the motherboard.

I'd just get a cheap PCIe to M.2 NVMe SSD adapter(s) for this.  Something like this (I/O CREST SI-PEX40110), also available here branded as SYBA SI-PEX40110.  Combine with a heatsink like this (2-pack, single here).  My experience with this combo here.  Or, choose from the myriad of other offerings.

Whether you could combine the NVMe SSDs with RAID, I wouldn't know.

I can install an M.2 hard drive WD Green™ SSD M.2 2280 - 240GB Model number: WDS240G3G0B. To the bay to the Precision 3630 Tower.
I see that you have an m.2 slot on the motherboard