Need help selecting hardware for first rig

Hey everyone.

I need everyone's opinion/advice for selecting the hardware for my first rig. To describe what I'm looking for, I'm going to ask some questions, and state some facts about equipment availability and prices.

Please go through the information, and let me know your thoughts. I know it may be a long post, so I really appreciate your responses.

Here is some basic pricing in my country. These values are in my country's currency (INR) as opposed to dollars, since equipment here is generally more expensive than in the US. I've added dollar values of the final rigs, for the readers' convenience.

PSU

Brand/Model	Rating	Price
Antec HCP 1300 platinum	1300W	INR 22,500

Seasonic X 1250 80+ Gold	1250W	INR 18,500
Seasonic SS 1000XP Platinum	1000W	INR 17,950
Seasonic X 1050 Gold	1050W	INR 14,950
Seasonic 860 XP2 Platinum	860W	INR 15,499

Corsair AX 1200	1200W	INR 21,500
Corsair HX 1050 80+ Gold	1050W	INR 16,250
Corsair AX 860 Platinum	860W	INR 15,000
Corsair HX 850	850W	INR 12,626
Corsair HX 750 80+ Gold	750W	INR 10,650

GPU

Brand/Model	Price (INR)
MSI R9 280X	INR 26,500
Sapphire Radeon R9 280X Dual-X OC	INR 25,000
Sapphire Toxic R9 280X	INR 29,000

Now, the reason behind these detailed tables is for the readers to notice that the high rated PSUs will cost me almost as much as the GPUs. We'll keep this observation in mind while we build the rig.

Another thing to keep in mind is that the computer (MoBo + Processor [AMD Sempron 145] + RAM [4GB 1600 MHz Corsair/GSkill] + Pendrive [for storage] + other misc items) will cost me roughly INR 30,000
I'll add a Sine wave inverter to this for protection against power surrges or power loss. This will cost me an additional INR 10,000
So total cost of 1 Rig (without PSU and GPU) = INR 40,000 (Which is quite significant)

Now, regarding the build itself:

I'm planning to work with R9 280x cards. I'll start off with 2 cards, and eventually build it up to 6 cards in the rig. Regarding this, I have a few questions:
- Someone suggested that I split this between 2 rigs, so as to not keep all my eggs in one basket. I definitely understand the wisdom in this; however, knowing the fact that a computer alone will cost me as much as roughly 1.5 GPUs or 2 PSUs, would you suggest that I go for two rigs or one?
- How much power will I need to run 6 cards eventually? The highest available PSU in the market is 1200W. I don't think this will be enough. So eventually, I'm going to have to add a secondary PSU anyways. Keeping this in mind, what should be the rating of my PSUs? 2x 860W or 2x 1000W or 2x 1200W ? Note that I will try to under-volt the cards, but I don't want to rely on this.
- Is Corsair better or Seasonic better for PSUs ?
- Does the Platinum/Gold make that much of a difference? I'm less concerned about the power draw off the wall, and more concerned about the safety of my hardware.
I was planning to use ASRock 970 Extreme 4 as the MoBo, but I read on a thread that it only supports up to 5 GPUs. Which MoBo can I use for 6 cards if I decide to go for the one rig option?
- Related to this question, the ASRock 970 Extreme 4 is an older board, if I'm not mistaken, and its availability is dicey. Which MoBo is everyone using these days for their rigs?

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If I decide to go with multiple rigs option, then I'll try to fit 4 GPUs in one rig. With 280x cards, I think I need more than 1200W on each rig, in this case too.

So we have several options available:

2 rigs with 4 cards and 2 cards (Eventually, I can add 2 more cards to the 2 card rig, when I decide to expand more)

Rig 1: Computer cost (40,000) + 2x 860W PSU (Seasonic:: INR 15,500) + GPU cost (4 x 26,500). Total= INR 180,000 ($2920)
Rig 2: Computer cost (40,000) + 2x 860W PSU (Seasonic:: INR 15,500) + GPU cost (2 x 26,500). Total= INR 127,000 ($2060)

Important note: Since I can't run 4 cards in 1200W, and I'm going to have to go with a dual PSU setup for every rig. For a 4 card set up, I think 2x 860W should suffice. Please correct me if I'm mistaken.

Total for 2 rigs = $4980 (approx.)

2 rigs with 3 cards each

Per rig Cost: Computer cost (40,000) + 1200W PSU (Seasonic/Corsair/Antec :: 18,500 / 21,500 / 22,500) + GPU cost (3 x 26,500). Total= INR 138,000 to INR 142,000 ($2240 to $2300)

So, for 2 rigs, total = $4500 to $4600 (approximately)

Important note: I'm not particularly fond of this setup since I only have 3 cards per rig. If I go up to 8 cards, I'll have to start another rig. Which will cost me more. Another option is to use the previous set up, which has the option to add 2 more cards without any increase in cost for computer components.

1 rig with 6 cards.

Rig 1: Computer cost (40,000) + GPU cost (6 x 26,500). Total= INR 199,000 ($3220)

The PSU cost needs to be added.

2x 860W : INR 34,000 ($550 :: including one add2psu component)
2x 1000W : INR 33,000 to INR 39,000 ($535 to $630)
2x 1200W : INR 40,000 to INR 46,000 ($650 to $750)

Total cost of rig: $3770 (with 2x 860W) to $3970 (with 2x 1200W)

As you can see, this setup saves me $1000 easily.

So, what are your thoughts / comments / advice? Also, please don't forget to answer the questions mentioned above.

Thanks a lot for going through this painfully long post!

Happy New Year!