I would not install an SSHD in a RAID. Personally, I wouldn't use an SSHD as a matter of principle, because although you have the advantages of both technologies up to a certain point, you also have all the disadvantages and risks of HDDs and SSDs. I have not had any bad experiences with WesternDigital HDDs so far (12+ in private PCs and at least as many in the shop-->only one defect).

What do you mean by connect? That is basically not possible. This is a stand-alone drive. Use together? Yes. However, as always, you need two separate connections and cables for this.

Hi, Can you still tell me your motherboard? Some motherboards disable Sata ports because of the PCI-e lanes. Have you tried other Sata ports?

This question is more about which disks are compatible with your Mac and not the other way around. Only Apple will be able to tell you, or you can play guinea pig yourself.