It depends on what plans you have for the rig. If just want to start mining as soon as possible, as mentioned a 650W would be plenty for up to 7 460 cards. Stick with EVGA or Corsair Gold or Platinum rated models. The EVGA 650W P2 is a great choice for under $100:

https://www.newegg.com/Product/Product.aspx?Item=N82E16817438055

The EVGA 750W P2 or G2 is also a good choice and it comes with twice as many VGA ports. Once you upgrade to better cards you can daisy chain a second PSU and have less out of pocket than a single larger PSU. If you want to wait, RX 570/580 should be more available in a week or two.

If you want to use Windows, an OEM license is available on eBay for less than $5. Any cheap 64GB SSD is enough. If you want to use smOS, a flash drive is sufficient.