Should I get a dedicated RAID card?

Normally, I'd say the money the cost is totally not worth it. And even less for a PC, and not for a workstation.

I'd say, stay with your mobo integrated controller. The difference won't be THAT big. No as big as 400$.

Yea, especially since any difference between RAID controllers would be cheaper to just get a third drive.

You most likely won't notice any kind of performance boost unless you are using several SSDs.

For Two drives, no

For 4+ HDDS yes

Unless you're planning on RAID 1,5,10, etc, don't. Complicated RAID levels will place additional stress on CPU.. RAID card removes that stress to a dedicated controller

RAID 0, shouldn't even consider a dedicated RAID card unless +4 drives