Vertikull

Yes, 290x 4gb from any vendor will do. In fact 290x 8gb and 390x will work at CF with your card as well, though they will work as if they only have 4GB VRAM

would you be willing to trade your card for my 1060 . . .

Good catch, I forgot about the controller part.

SAS controllers work with SATA drives, but not the other way around, SAS drives do not work with SATA controllers.
What OP needs to use his drive is a SAS controller (SAS is server grade, hence drives and controllers are expensive).
I would say that OPs best option is to return his SAS drive and get a SATA drive instead.

You bought a SAS drive. There are definitely SAS to SATA adapters out there, just search around.
 

jayz2cents is your guy, he has multiple tutorials. Theres also technique videos to get you started with part selection.

click on your name (top right) Account Settings --> Signature

I've had plenty of experience with Dual GPUs:

2x ATI Radeon HD 4870s in Crossfire.  At the time, two of these were a good deal faster and cheaper than a single Nvidia GTX 280.  Bought both from the get go.

2x Radeon HD 7870s in Crossfire.  I started with a single HD 7870 which served me well and added a second down the line when I found a really good deal on a second card.

2x GeForce GTX 970 in SLI.  Again, started with one card and added a second down the line when certain titles I played were not performing as well as I wanted them to.  At the time, 2 970s in SLI easily outperformed a GTX 980ti and costed less.

In almost every instance I've used mGPU, two mid/high tier GPUs outperformed the highest performing single GPU for less money.  Also, adding a second card down the line when I needed it helped me add more performance for far cheaper than buying a single GPU solution.  I think with the exception of Nvidia's 10 series, this has always been true, I don't think 2x GTX 1070s outperform a 1080ti.

That being said I have had problems.  Some games straight up don't support SLI/Crossfire.  For me, the games that do not already run extremely well with a single GPU.  Scaling isn't always perfect and you don't always get good support on day one.  Nvidia is actually a lot better than AMD/ATI was at getting an SLI profile out on day one, but it's hit and miss sometimes.  Also, some graphical features are incompatible with dual GPU setups.  Deus Ex Mankind Divided for example, the temporal AA method used in the game is utterly broken for dual GPU leaving you with limited options for effective antialiasing.  Heat and noise, an SLI setup is easily going to put you in the 300-400W under full load range and one card is going to be about 10 degrees hotter than the other and its fan is gonna ramp up constantly.  My GTX 970 STRIX cards were virtually silent even when overclocked and run as a single card, but in SLI one card always ran hot and ramped up the fan.

Lastly, I just gave up my SLI setup because the latest Windows 10 update broke the way my motherboard allocated PCIe lanes to two cards.  This isn't a fault of SLI/Crossfire itself, but when you have more components in a system you're likely to encounter more issues.  That's just true of any system.

In conclusion, there are some quirks, but depending on pricing and timing you may be able to get flagship like performance at a cheaper price, or add some extra power down the line when you need it.  Just depends on your needs for the system and what you can afford at the time.  I don't regret using dual GPU, but I wouldn't go back to it if a single GPU solution makes more sense economically/financially at the time.