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=N82E16817438055The 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.
Gotcha....so the OEM license. Is that buying just the license and me already having a install disk. Then during the instal when it ask for the license key I enter that one in?
Also can I run 7 cards on the 650w P2 PSU? I probably will only run like 4 or 5 at first but just wondering how many physically I could run, not wattage wise as you said it would run 7
When you buy the OEM license on eBay, the sellers provide a link to download the ISO if you don't have one. You can use that to create a boot flash drive using Rufus. If you plan on using 6+ GPU's, you must install Windows in UEFI mode. Make sure to select GPT disk for UEFI from the Rufus menu when creating the install flash drive or you can select the cd UEFI boot in the motherboard boot menu.
The RX 460's without the PCI-E power connectors should use less than 50 watts each as BBT shows in the video. How many cards you can put in a rig is limited by what the motherboard supports. Most motherboards have less than 6 PCI-E slots. The ones that have 6 or more, do not always work with that many cards or are a pain to setup, so it's important to stick tp motherboards that are known to support 6+ cards.
You also need to get a power usage meter to check how much power is being used by the rig and make sure it's efficient.
https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU